A robot lawn mower is the only smart home device that does an hour of physical work for you every week. Instead of cutting the whole lawn at once, it trims a few millimetres off the grass several times a week and drops the clippings back as mulch, so the lawn stays at a constant height and never looks like it was just mowed. The machines have changed faster than almost any other outdoor category: the buried boundary cable that defined them for twenty years is now optional, and the models launched in the last two seasons find their way around a garden with satellites, cameras and spinning lasers.
That change is also what makes them hard to compare. Two mowers at the same price can differ by a factor of three in the lawn they cover, by 50 percentage points in the slope they climb, and by whether they need an afternoon of cable pegging or fifteen minutes with a phone. The specs below are the ones that actually separate them.
Start with the size and shape of your lawn
Max Mowing Area is the first filter. Manufacturers rate it in square feet or square metres of real grass, so measure the lawn, not the plot: driveways, beds, the pool and the house do not count. A quarter acre is about 10,900 sq ft and a full acre about 43,560 sq ft. The rating assumes the mower can run most days, so if your garden is close to a model's ceiling, a rainy week or a broken session will leave you behind. Picking one size class above your lawn is cheap insurance.
Mowing Efficiency, given in square metres per hour, tells you how long a session takes. Small vision-guided mowers cover around 120 m²/h, while large systematic ones reach 500 m²/h and more. Combined with Cutting Width, it decides whether the mower is done before breakfast or still working at noon.
Shape matters as much as area. A garden split into a front and back lawn needs either Multi-Zone Mapping or a mower that can drive between the zones on its own, which is what Obstacle Crossing Height describes. And check the mower's Dimensions against your narrowest gate: a 17-inch deck does not fit through a 15-inch side passage.
Navigation is the decision that costs the most
Navigation Type is where the money goes, and it comes in four flavours that current models mix freely.
- No Perimeter Wire models skip the boundary cable entirely. You set the garden up by walking the mower around it once or by letting it map on its own, and you redraw the boundary in the app whenever a bed moves. Wired mowers are cheaper and very reliable, but installation takes a day and the cable is one spade stroke away from a repair job.
- RTK Positioning corrects satellite position down to about 2 cm using a fixed antenna, usually on a mast with a clear view of the sky. It produces the straight, overlapping stripes these mowers are known for, and it loses accuracy under dense trees or against tall walls. Some models replace the local antenna with a network RTK service delivered over 4G Cellular.
- Camera navigation reads the grass and the surroundings directly. It removes the antenna and the wire, which is why the cheapest wire-free mowers use it, but glare, deep shade and dusk are still hard for it.
- LiDAR Navigation maps the garden in 3D with a spinning laser. It does not care about satellites or daylight, so it keeps working under trees, along fences and at night, which is exactly where the other two struggle. It is the main reason the premium tier costs what it does.
Whatever the positioning, AI Vision Obstacle Avoidance is what keeps the mower off hoses, toys, fallen fruit and sleeping animals. Without it the mower finds obstacles by bumping into them, and No-Go Zones drawn in the app become the only protection your flower beds get.
Slopes, traction and rough ground
Max Slope is quoted as a percentage: 45% rises 45 cm over a metre, roughly 24 degrees. Entry models stop near 30%, mid-range two-wheel-drive units reach 45% to 50%, and all-wheel-drive machines climb 80% and beyond. The ratings assume dry grass, so leave headroom for the steepest, wettest corner of your garden.
Drive Type is the other half of the answer. Two-wheel drive is lighter, cheaper and perfectly adequate on flat and gently rolling lawns. All-wheel drive earns its premium on banks, ruts, thick thatch and wet grass, and it is usually paired with a heavier chassis, which also shows up in Weight.
The cut itself
Cutting Height is a range, and your grass type decides where you need to sit inside it. Fine ornamental lawns are cut around 1 to 1.5 inches; shaded, drought-prone and most warm-season lawns are healthier at 3 inches or more. Verify the range covers what your lawn needs, and check Cutting Height Adjustment: app-controlled height lets you lower the cut before a party and raise it during a dry spell without walking to the mower, and it allows a different height per zone.
Edge Cutting is the feature owners most often wish they had bought. A standard blade disc sits inside the wheels, so a strip of a few centimetres survives along every wall and bed, and you finish the job with a string trimmer. Mowers with an offset disc or a dedicated trimmer arm cut to the border themselves.
Blade System decides maintenance. Small pivoting razor blades are cheap, fold away on impact and need changing every few weeks; a rotary blade or a dual blade disc handles tall and wet growth and leaves a cleaner finish.
Battery, sessions and the season
Battery Life between 60 and 220 minutes is normal, and a short runtime is not a defect in itself, because the mower recharges and resumes on its own. What matters is the pair: Charging Time of 50 minutes after a 90-minute cut gets through far more lawn per day than 180 minutes after the same cut. A Swappable Battery turns a worn pack after a few seasons into a cheap spare part instead of the end of the mower.
Weather Resistance should be IPX4 as a minimum and IPX5 or better if you plan to rinse the mower with a hose, and a Rain Sensor keeps it off soaked grass, which tears rather than cuts.
Safety, theft and the smart home
Lift & Tilt Sensor support stops the blades within a fraction of a second and is close to universal; Pet & Child Detection is not, since only camera and LiDAR models can tell a toddler from a fence post. An Emergency Stop Button is required in several markets and is the fastest way to halt the machine in person.
A mower is a four-figure machine parked in an open garden, so GPS Tracking, a PIN Code Lock and an Anti-Theft Alarm are worth checking as a group. Tracking works best on models with their own cellular link, because a stolen mower leaves WiFi range in seconds.
Finally, the smart home side. Most mowers connect over 2.4 GHz WiFi, and the honest question is whether your network reaches the far end of the garden at all, the same coverage problem outdoor Cameras run into. Alexa and Google Home support is common for start, stop and return commands, Home Assistant support varies between an official integration and a community add-on, and Matter is only now arriving in the category. If you already run a hub-centred setup with Hubs and scheduled irrigation through Water Valves, check Automations support so the mower pauses when the sprinklers start.
