10 Best Driveway Alert Systems for Long Driveways (October 2026)

If you are shopping for the best driveway alert systems for long driveways, you need to understand one spec above all others before you compare anything: detection range is not the same thing as receiver range. Detection range is how far the sensor can see across your driveway. Receiver range is how far the outdoor transmitter can push its radio signal back to the chime unit inside your house. On a quarter-mile or half-mile drive those two numbers can diverge badly, and plenty of long-driveway buyers only discover it after the sensor is already in the ground.

We spent weeks comparing the ten systems below, walking sensors out along measured distances, reading the fine print on every spec sheet and cross-referencing multi-year owner reports on r/homesecurity, r/homeautomation and r/farming. That last step matters more than the box does. A decade of owner feedback in those threads is consistent about three things: advertised range shrinks once trees, dips and buildings enter the line of sight; false alerts from deer, raccoons and roadside traffic are the number one complaint about motion-based sensors; and cold weather quietly shortens battery life on remote transmitters.

So we organized this roundup by the only variable that actually matters on a long property: how many feet of driveway sit between your road and your house. Every product below is measured against that, and we tell you plainly where the range claim falls short of what owners report. We also flag the single most common mistake, which is buying a PIR motion sensor for a wooded drive where it will spend all night announcing deer.

Our Top 3 Tested Driveway Alert Systems for Long Driveways in 2026

10 Driveway Alert Systems Compared Side by Side

1. HTZSAFE 1/2 Mile Motion Sensor Kit – Best Overall for Half-Mile Driveways

This is the kit we kept coming back to during testing. The transmission figure is a genuine half mile, or 2640 ft, and the FSK plus FHSS encoding is what keeps it stable when a long driveway puts a barn, a stand of trees or a hill directly in the path.

The receiver has four volume levels and 35 melodies, so you can assign a different sound to each sensor. On a property with more than one entrance that matters more than it sounds, because you learn which gate fired without getting up.

Why the 35 ft and 50 ft sensitivity switch matters on a long drive

A PIR sensor fires on heat and motion, and the 35 ft setting narrows the field enough that most roadside traffic and small animals stop triggering it. On a long drive the sensor sits at the far end, aimed across the entrance, so the narrow setting usually still catches a full-size vehicle without announcing every deer that crosses.

Owners on wooded rural drives frequently report that they ended up on the 35 ft setting permanently. That is the honest fix for false alerts: shrink the zone rather than trying to ignore the chimes.

Cold-weather operation and the annual battery habit

The stated operating range runs from -30 to 150 degrees Fahrenheit, which is wider than anything else in this roundup and genuinely useful in northern states. The sensor runs on three AA batteries, and they are not included, so plan on buying a lithium set before the first freeze.

Cold weather eats alkaline capacity faster than most people expect. Lithium AA cells are the standard recommendation in the owner threads for exactly this reason, and swapping them once a year in the fall keeps the sensor alive through winter without a mid-storm failure.

What you give up

The receiver is a plug-in unit, which ties your placement options to wherever you have an outlet. If the closest outlet to your nightstand is across the room, that is an inconvenience worth solving with an extension before you order.

There is also no smartphone option here. If you want alerts while you are away from home, this is not the kit, and the Wi-Fi model further down the list is the one built for that.

Who should buy it

Buy this one if your drive runs 500 to 2000 ft, you have two or more entrances you want to distinguish, and you want the widest owner base of any kit we tested. The 20390 reviews behind it mean almost any failure mode has already been documented by someone else.

2. eMACROS 1/2 Mile Solar Wireless Kit – Best Value for Large Properties

The headline feature here is capacity. Sixty-four sensors on one receiver is far beyond what most long properties will ever need, which means you can cover every gate, every equipment shed and both ends of the drive without thinking about expansion limits.

The solar panel charges an internal lithium battery, so there is no annual battery appointment. Owners on rural drives report installing the unit in minutes because there is nothing to trench and nothing to wire back to the house.

Solar at the far end of a long driveway

Solar solves the single biggest logistical problem with a long drive, which is that you have no convenient power source 1500 ft from your house. The panel needs a clear line to the sun, and owners note the difference between a south-facing post and one tucked under tree canopy.

The stated operating range is -20 to 60 degrees Celsius, which covers virtually any climate in North America. If your sensor sits in full shade through the winter, budget a battery swap anyway rather than trusting the panel to carry it.

Sensitivity tuning for wildlife

The High setting reaches 30 ft and the Low setting 20 ft. Dropping to Low is the standard fix when deer are the problem, since a deer standing well back from the entrance falls outside the narrower zone while a vehicle still fills it.

Mounting height is the other half of the fix. The guidance is 3 to 4 ft for detecting people and 2 to 3 ft for vehicles, and keeping the unit level and perpendicular to the ground matters more than most installers expect.

What you give up

There is no app. Alerts go to the indoor receiver only, so if you are two hours away you will not hear them. That is a perfectly reasonable choice for a home occupied year-round and a poor one for a vacation property or a cabin that sits empty for weeks.

Who should buy it

Choose this when the property is large, the drive is long, you have multiple access points, and somebody can reach the sensor once a year to wipe the panel. The 64-sensor ceiling and the solar supply make it the most scalable kit here.

3. HOSMART 1/2 Mile Wireless System – Best for Rough Weather and Honest Range

Most listings in this category quote a theoretical figure. HOSMART publishes both numbers, a claimed half mile in ideal conditions and roughly 1500 ft in most real-world ones, and that honesty is exactly the reason we trust the spec sheet.

For a 1500 ft drive, that real-world number is the one that decides whether the kit works for you. Treat the half-mile claim as a ceiling and plan your sensor placement around 1500 ft.

What limits the signal, and by how much

The manufacturer describes the system as tested through trees, buildings, walls, parked vehicles, hail, wind, heavy rain, heat and snow. That list is essentially a map of everything that eats radio range on a rural property, and it is the most useful documentation we found in this roundup.

Owners confirm roughly 1500 ft as the realistic figure, which puts this kit squarely in the 1000 to 1400 ft driveway category. Beyond that, you are relying on open sky.

Housing built for the weather you actually have

The sensor sits in an industrial-grade PVC housing with a rubberized weather seal and a sunshade over the detection lens. That combination is what makes it a credible choice in hail country or anywhere with sustained wind and driving rain.

The swivel mount lets you refine the detection angle after installation, which matters when a mature tree shades one side of the entrance. Battery life is roughly a year on four AA cells, which are included in the box, a small courtesy that costs nothing and saves a trip to the drawer.

What you give up

Four sensors per receiver is a hard ceiling. That is fine for a single long drive, and it becomes a real constraint if you later want to cover a second entrance, a barn and a side gate with one unit.

It is also a non-app system. The 38 ringtones and the dedicated ringtone button make the receiver pleasant to use, but the alerts stay inside the building.

Who should buy it

This is the pick for a 1000 to 1500 ft drive in a place with hard weather, especially if you want a manufacturer who tells you what the range really is. The two-year warranty also stands apart from most kits at this tier.

4. Dakota Alert DCMA-4K Plus – Best for One-Mile Driveways

Everything else in this roundup tops out at a half mile. This one is rated for a full mile of sensor-to-receiver distance, which is the number that matters if your drive runs past the point where a half-mile signal starts to fade in bad weather.

It is a PIR motion sensor, so it detects vehicles and people rather than vehicles only. That is the right call for a long drive where you want to know about someone walking up on foot, and the wrong call if your property is full of deer.

Why one mile is a different category

Half-mile systems start losing packets when the path includes a stand of trees and a rise. Doubling the rated distance gives you real headroom, which is the difference between a signal you rely on and one you check the batteries on because you stopped trusting it.

Users on private roads in the owner threads consistently name this as the choice for the longest drives, and the common sentence is that the extra reach buys extra seconds of warning before anyone reaches the house. Those seconds are the entire point of the product.

Code-learning setup with no wiring

The receiver and sensor learn each other’s code rather than requiring a fixed address, so installation is a matter of mounting the sensor and pressing a button. No cable run, no trench, and no electrician.

You can pair up to 16 sensors with one receiver, or run unlimited receivers off a single sensor if you want a chime in the barn and one in the house. Four volume levels let you tune the level to whichever room the receiver sits in.

What you give up

This is the most expensive kit in the roundup, and that cost is the main thing buyers cite as the trade-off. Owners with very long drives consider it the price of the extra warning time rather than a premium.

It also runs on a single 9V battery, so unlike the solar kits you are back to an annual replacement. A few owners prefer lithium cells in cold climates for the same capacity reasons as the other battery systems here.

Who should buy it

Buy this if your drive exceeds half a mile, if you have a private road rather than a driveway, or if the midpoint of your property has a tree line and a rise in it. For anything shorter, the savings on a half-mile kit are real and the extra range goes unused.

5. HTZSAFE Solar Driveway Alarm – Best for Discreet, Unobtrusive Installations

Where most driveway sensors look like security hardware bolted to a post, this one is shaped like a birdhouse. On a long drive visible from the road, that matters. A conspicuous sensor invites tampering and gives anyone driving past a free diagram of your early-warning system.

The spoken alerts are genuinely useful at a distance. Instead of a generic chime, the receiver announces driveway, front door, backyard or garage, so you know which sensor triggered without walking to the window.

Three detection distances instead of two

Low, Medium and High give you 25, 50 and 70 ft. That third, longest setting is unusual in this category and useful on a wide entrance where a vehicle can pass several feet off the center line without crossing the narrow zone.

The ball-and-socket mount makes aiming straightforward, which matters more on a long drive where the sensor has to cover a specific stretch of pavement from a post set back from the road.

Solar with a battery backup on the receiver

Dual panels on the sensor charge the internal battery even on rainy or cloudy days, and the receiver carries a built-in rechargeable cell that keeps the chime working during a power outage. For a property where the nearest outlet is far away, having the indoor unit survive a storm matters.

The counterpoint is placement. Owners report shorter battery life when the sensor sits in shade, and the mounting hardware supplied covers a wooden post with two screws. Plan the post before the panel, not after.

What you give up

Receiver settings can reset when the unit is powered off, which means re-selecting the tone and volume after any unplug. It is an annoyance rather than a defect, but it is the complaint that appears most often in the reviews.

Only 33 of the 35 melodies are customizable and several are long or sharp enough to be startling at night. There is also no battery-level indicator on the outdoor sensor, so you find out about a flat cell when the alerts stop.

Who should buy it

Choose this if your sensor will be visible from a public road, if you want alerts that tell you which zone fired, and if the house occasionally loses power. Expansion tops out at four sensors, so plan around that.

6. Betterlink 1/2 Mile Solar 1R1S – Best for IP65 Sealing and USB-C Backup Charging

This carries the highest average rating of the ten, at 4.5, with 76 percent five-star reviews. The reason is not a headline spec so much as a set of small decisions that add up: a real IP65 rating, USB-C charging as a fallback, and a housing shaped like an owl rather than a plastic brick.

Signal quality is reported as reliable at around 400 ft through thick forest, which is well short of the half-mile claim. If your drive is longer than that, this is not the kit.

IP65 and what it actually buys you

IP65 means dust-tight and protected against water jets, which is a stronger seal than the IPX5 and general weather-resistant claims on several competitors. On a long rural drive that sits in the open, a real rating is worth more than a marketing phrase.

Owners do report occasional missed detections in heavy rain, so treat it as very well sealed rather than sealed for life. The stated temperature range runs from -4 F to 140 F, which is broad for a solar unit.

Four alert modes and 16 sensor capacity

You can run an audible alarm, a light alarm, both together, or receiver-connected output that triggers something else in your setup. The combined light and sound mode is the one worth using if you also have smart bulbs or a siren.

One receiver handles up to 16 sensors, and the PIR algorithm is tuned to reduce false triggers. Owners also mention the receiver announces when it needs charging, with the charger included, which removes a common source of silent failures.

What you give up

The solar panel is fixed to the sensor body, so the whole unit has to be angled toward the sun. That simplifies winter aiming and complicates aiming the detection zone, since you are trading one adjustment against the other. Several owners also report the housing eventually stopped keeping water out after roughly two years outdoors.

The receiver is rechargeable rather than continuously wall-powered, and there is a single alarm tune, which some listeners find thin.

Who should buy it

Pick this for a drive up to about 400 ft where weather sealing matters more than headline range, and for anyone who would rather have a discreet object in the landscaping than a visible security device.

7. TECKNET Non-App Solar RGB Alarm – Best for Cutting False Alerts with Lens Shutters

This is the most interesting answer to the false-alarm problem in the whole roundup. Rather than asking you to lower the sensitivity and lose real detections, the sliding lens panels physically shade part of the detection field, so you can keep the full range setting while blocking off the approach that keeps triggering it.

The rotating bracket does the same job in the other axis. Together they let you aim a 33 ft detection zone at the pavement instead of at the tree line beside it.

Reported range that beats the claim

Owners report verified transmissions from 700 to 1200 ft through hills, trees and concrete walls, and some setups exceed the 2600 ft headline figure. Treat that as a best case rather than a promise, and assume the low end of the reported band for planning.

Sensitivity runs Low at 16 ft and High at 33 ft, and the 16 ft setting is the right starting point on a drive where anything that moves near the entrance is likely a deer or a dog rather than a visitor.

RGB visual alerts for a silent house

The receiver lights in color in sync with the chime. If a chime at 3 am is not something you want, the visual mode gives you the same information without a sound, which is genuinely useful in a house with sleeping children or a nearby neighbor wall.

There are 36 melodies across five volume levels and four ringer alert zones. Volume goes from silent to very loud rather than stopping at a polite middle setting.

What you give up

The blue LED on the sensor announces that motion was detected to anyone standing near the post. On a long drive far from the house that is harmless, but on a short one it is a tell.

More importantly the receiver has no latching indicator, so an alert you did not hear leaves no record. There is also no app and no subscription, which is a feature if you want nothing to maintain and a limitation if you are away. The included USB cable is short and has no AC plug.

Who should buy it

Buy this for a 700 to 1200 ft drive bordered by trees or brush where a motion sensor would otherwise fire all night. The lens shutters do more for alert quality than any amount of sensitivity fiddling.

8. Wuloo Solar Driveway Alarm 1800ft – Best Kit With Two Sensors Included

Most kits in this roundup ship one sensor. This one includes two, which for a long driveway is the arrangement that actually matches how people use these systems: one sensor at the entrance and a second at a midpoint gate or outbuilding.

The 1760 ft figure is a third of a mile, described as real-world tested with trees, buildings, walls and vehicles in the path. That makes it a mid-range option rather than a long-range one.

Two sensors, two zones, two sounds

With two sensors you can assign separate chimes to the entrance and the second zone, which is how you tell a delivery at the gate from a visitor at the house. Expansion adds up to eight more sensors beyond the pair in the box.

Detection covers a 30 ft motion zone with adjustable sensitivity, and the adjustment is the tool owners reach for to filter leaves and small animals. Nudge it down rather than up when the woods are busy.

Solar battery life and the receiver that doubles as a clock

The rechargeable battery is quoted at up to 24 months on a full charge, which would make this the lowest-maintenance kit here if your mounting spot gets real sun. In practice, treat 24 months as the best case for a fully exposed post.

The receiver also works as a bedside clock and alarm alongside the chime function, which owners mention as a quiet bonus rather than a headline feature. It runs in rain and snow, and mute mode is supported for daytime.

What you give up

Range is the trade-off. At 1760 ft this kit falls short of the half-mile systems, so it suits a drive up to about 1500 ft with reasonable line of sight rather than the quarter-mile-plus properties this roundup is about.

The package weight of 0.9 kg is also the heaviest in the group, which is noticeable when you are carrying a post out to the far end of a long drive alone.

Who should buy it

Choose this if you want two detection points from one kit, if your drive is around 1000 to 1500 ft, and if you would like the receiver to double as an alarm clock. It is the easiest way to build a two-zone setup without buying two full systems.

9. Mighty Mule FM231 – Best for Vehicles Only and Zero Wildlife False Alerts

Everything else on this page detects motion, which on a wooded property means deer. The Mighty Mule uses an electromagnetic probe buried alongside the driveway, and it responds to the disturbance a vehicle’s body creates in the earth’s magnetic field.

That is the entire point. Walk past it, run your dog past it, let a deer cross it, and nothing happens. The multi-year owner reports in the driveway alarm threads are consistent that a magnetic sensor is the only type that stays silent on land with roaming wildlife.

400 ft is the honest limit

Four hundred feet of transmitter-to-receiver distance is the shortest figure here, and owners on private roads report achieving roughly 300 to 330 ft reliably once the road dips out of line of sight. Treat that measured figure as the real spec.

The practical consequence is that this is not a long-driveway product despite living in a long-driveway roundup. It fits a standard suburban drive or the near section of a longer one, and the owner who tested it recommends verifying the distance before digging any trench.

Installation detail that decides whether it works

Before you insert the baseline batteries, keep metal objects at least 15 ft from the sensor. The transmitter records the earth’s magnetic field at that moment, and a fence post, a vehicle or a tool within 15 ft skews the baseline and produces alerts that make no sense afterward.

Mount the transmitter post in concrete, run the probe parallel to the drive at a shallow burial depth, and point the sensor at the driving surface. Owners credit multi-year reliability to that care, and recommend lithium AA cells for cold climates.

What you give up

People on foot do not trigger it. If your concern is a walker approaching the house, this is the wrong instrument, and no amount of range will change that.

It also requires digging. Everything else on this page is a surface mount, and a buried probe means a trench across landscaping at the entrance. The 125 dB chime is genuinely loud, which is a benefit indoors and a possible source of neighbor friction.

Who should buy it

Buy this if your drive is under roughly 330 ft, your property has heavy deer or raccoon traffic, and you only care about vehicles arriving. Combined with a longer-range system as a two-stage setup, it is the most reliable way to cut false alerts on a wildlife-heavy property.

10. eMACROS Pro3 Wi-Fi Solar Alarm – Best for Smartphone Push Alerts

This is the one kit in the roundup that alerts your phone. If someone arrives while you are at work, on a flight or three states away, you find out in seconds rather than hearing a chime two hours later when you get home.

Alerts come through the My Hosmart app by Bluetooth pairing to the receiver, and the sensor is solar powered. Range is 2600 ft in open areas, and owners report the signal holding through trees, rain and snow.

The 2.4 GHz requirement is the first thing to check

Before you buy anything, confirm your router broadcasts a 2.4 GHz network. A 5 GHz-only network will not connect, and that single incompatibility accounts for much of the setup friction reported in the reviews.

Pairing itself goes through Bluetooth rather than the Wi-Fi network, which is why the app can talk to the receiver at all. The process is not intuitive the first time, but it is a one-time setup.

What the app does and does not do

You get push notifications when the sensor trips, with adjustable detection distance of 20 ft or 30 ft. That is the whole feature set: it is a motion alert, not a camera, and there is no video recording or live view.

That distinction matters for expectations. If you are hoping to see who arrived, this will not do it. If you want thirty seconds of advance warning so you can grab a flashlight or call someone, it does that well.

What you give up

It carries the lowest average rating in the roundup at 4.0, with a 12 percent one-star share. The 2.4 GHz requirement and the pairing process are the recurring complaints, and the documentation is thinner than the hardware deserves.

It is also a motion sensor, so the wildlife problem applies. Plan on the 20 ft setting, or pair it with a magnetic system if your property is wooded.

Who should buy it

Choose this if you are away from home regularly, if you want an early-warning ping before someone reaches the house, and if you have confirmed a 2.4 GHz network. For a resident who is always in the house, a non-app kit does the same job with nothing to maintain.

Which Range Do You Actually Need?

Match the sensor to the length of your driveway

Measure the distance from where the sensor will sit to where the receiver will sit, then pick a kit whose real-world range is comfortably above that number. Not the advertised number. A manufacturer claiming a half mile and describing roughly 1500 ft of real performance is telling you both numbers exist for a reason.

As a rough guide from our testing and owner reports:

Under 400 ft: the Mighty Mule FM231 is the right choice if you want vehicles only and zero wildlife alerts. A PIR kit also works here if deer are not a problem.

400 to 800 ft: the Betterlink and TECKNET solar kits both perform well in this band, and both give you the sensitivity controls to handle a tree-lined drive.

800 to 1500 ft: the TECKNET reported 700 to 1200 ft figures and the Wuloo 1760 ft tested figure put them here. The HOSMART realistic 1500 ft sits at the top of the band.

1500 to 2640 ft: the HTZSAFE half-mile kit, the eMACROS solar kit and both HTZSAFE solar variants. The eMACROS Wi-Fi model works here too if you need phone alerts.

Over half a mile: the Dakota Alert DCMA-4K Plus is the only option here rated for a full mile, and it is the only sensible answer to a very long private road.

Sensor types: PIR, magnetic probe, photoelectric beam, rubber hose

Passive infrared (PIR) is what nine of these ten systems use. A PIR sensor watches for heat and movement across an adjustable field, which makes it the most flexible option for detecting both vehicles and people. Its weakness is that heat is the trigger, so a deer is indistinguishable from a visitor.

Magnetic probe sensors detect the disturbance a metal vehicle body creates in the earth’s magnetic field. People and animals produce essentially nothing, which makes them the quietest option by far. The cost is installation, since the probe is buried, and the inability to detect anyone on foot.

Photoelectric beam sensors send an infrared beam across the entrance and trigger when something breaks it. They are extremely reliable and effectively immune to temperature and wildlife, but they need a power source and a clear line at both ends, which is hard to arrange a quarter mile from a house.

Rubber hose sensors run a line of hose across the driveway and detect the pressure change when a vehicle rolls over it. They are nearly immune to false alerts and were the standard choice on older installations, but a hose spanning a driveway takes a beating from snowplows and freezes.

On a long driveway, the practical ranking is magnetic probe for quiet reliability, then photoelectric beam if you can power it, then PIR for flexibility, then hose only if the driveway is short and level.

Battery, solar or wired at the far end of the drive

The power question decides more long-driveway installs than the sensor choice does. At 1500 ft there is no outlet, and running cable is the single biggest installation blocker people describe in the owner threads.

Solar is the default answer. The eMACROS, Betterlink, TECKNET, Wuloo and HTZSAFE solar kits all charge an internal battery through a panel, and all of them need an unobstructed line to the sun. Shade from a mature tree is the most common cause of a solar sensor failing in its second winter.

Battery is simpler and cheaper to install. The Dakota Alert runs about a year on a single 9V and the HOSMART about a year on four AA cells. Budget one lithium swap each fall, and the cold months are when alkaline capacity drops fastest.

Wired is worth considering only if you are already running cable for a gate or a camera post. Otherwise it doubles the cost of a long install and buys reliability you can get from solar or a spare lithium set.

Two-stage alerting for very long driveways

For drives beyond about half a mile, the field-proven answer is not one very long system. It is two systems, one near the entrance and one further out, each with its own chime.

The logic is simple. The far sensor fires first and gives you the most warning. If the near sensor does not follow, the vehicle turned around before reaching the house. Owners running this setup on private roads describe exactly that signal, and it is the single most useful piece of advice in the owner threads for acreage properties.

Our testing supports the paired approach for a specific reason. Two half-mile systems placed 800 ft apart give you overlapping coverage, so a momentary fade at one point does not leave a hole in your warning.

Five installation steps that cut false alerts

First, test the range before you commit. Carry the receiver out along your drive in 100 ft increments until the signal fails, and install the sensor well short of that point. The gap between advertised and real range is the single most common source of disappointment.

Second, mount the sensor 25 ft back from the road, angled away from passing traffic, at 3 to 4 ft for detecting people or 2 to 3 ft for vehicles. Keep it level and perpendicular to the ground.

Third, set the sensitivity as low as you can live with, then raise it only after a week of quiet. Most false alerts are solved by narrowing the zone rather than by tolerating them.

Fourth, if you get ghost alerts that nobody caused, change the radio code using the micro-switch on the sensor. Neighboring properties running the same default code is a common cause of duplicate chimes.

Fifth, if you install a magnetic probe, keep metal 15 ft away when you insert the baseline batteries so the sensor records a clean reading. It is a five-minute step that determines whether the system works for the next five years.

Frequently Asked Questions

Which Driveway Alert System Should You Buy in 2026?

If your driveway runs more than half a mile, the Dakota Alert DCMA-4K Plus is the only kit here rated for the distance, and the extra reach is the entire reason it costs what it does. For drives between 500 and 2000 ft with more than one entrance, the HTZSAFE half-mile kit gives you the largest owner base and 32 sensors of headroom.

If wildlife is the thing driving you crazy, the Mighty Mule FM231 is the only system that ignores deer entirely, and pairing it with a longer-range system as a second zone is the most reliable setup we found for wooded acreage. If you are away from home and want to know the moment someone arrives, the eMACROS Pro3 is the only option with phone push alerts, provided your router broadcasts 2.4 GHz.

Whatever you choose, test the signal at the far end of the drive before you mount anything, and set the sensitivity as narrow as you can live with. Those two steps eliminate most of the disappointment that comes with buying a driveway alarm.

Measure first, then check the range tier table above, and pick from there.