How to choose the best robot lawn mower

Robot lawn mowers are small battery-powered mowers, programmed to cut your lawn automatically on a regular schedule. They’re guided by navigation systems and use sensors to avoid obstacles.

After mowing or when the mower’s battery is running low, a robot mower will automatically return to recharge in its base station (also called a docking or charging station). The base station is plugged into mains power.

Robot mowers don’t have catchers that need emptying. Instead, they cut frequently, leaving behind a fine mulch that helps feed your lawn.

They’re typically not as good as standard lawn mowers at tackling rough terrain, long grass and more complex lawn shapes. And they usually cost more than a standard lawn mower.

However, once set up, robot lawn mowers don’t require the ongoing effort of using a regular mower.

Cleaning and maintenance

Robot lawn mowers are most like battery powered push mowers. They don’t emit fumes or need regular oil and filter changes like petrol lawn mowers.

• Every few days
  Remove debris from your lawn regularly. Objects like branches, twigs, leaves, stones and toys can interfere with mowing and damage your mower’s blades.

• Weekly
  Inspect and clean your robot lawn mower weekly. In particular, the sensors, blades and wheels must be undamaged and free from debris. And the battery contacts (on both the mower and charging station) must be clean and free from rust.

• Every 1–2 months
  Replace the mower’s blades every month or two, depending on how often the mower runs and the toughness of the lawn conditions.

• Yearly
  Most manufacturers require or recommend an annual winter service at a specialist service centre.

• Less frequently
  You’ll need to check for software updates from time to time. And you’ll need to replace the mower’s battery every few years, as is the case for any rechargeable tool.

Wire boundary robot lawn mowers

The base station of a wire boundary robot lawn mower is connected to a physical wire. The wire is laid around the perimeter of your lawn and around any ‘no-mow’ areas. It’s either pegged in place or buried just below the surface.

The base station sends a low-voltage current through the wire, creating an electromagnetic field. The robot mower’s onboard sensors detect this field and stop the mower leaving the mowing zone.

Basic models move around at random. More advanced wire boundary mowers use algorithms and/or GPS to mow systematically. (See Navigation and guidance systems.)

Physical boundary wires can be damaged and disrupt mower operation. They also need repositioning if you want to change your mowing zones.

Wireless boundary robot lawn mowers

Wireless boundary robot lawn mowers navigate within a virtual boundary. They use GPS and other guidance systems to stay within the mowing area and mow your lawn systematically. (See Navigation and guidance systems.)

Some also use artificial intelligence (AI) to identify and avoid a range of common garden features, people and animals. This technology can adapt if the environment changes.

Wireless robot lawn mowers are usually quicker and easier to set up. But tall trees and buildings, or being in a valley, can interfere with satellite signal. This can disrupt the mower’s operation. It can also affect location accuracy, meaning your mower could run into a pool or mow a flower-bed.

Most wireless robot mowers use several technologies to prevent such issues. However, a wire boundary model is better for properties that have poor satellite reception.

You can customise a wireless robot lawn mower’s boundaries and mowing zones or even move house without having to move any physical wires. And unlike wire boundaries, virtual ones can’t be damaged.

Suitability for your backyard

• Lawn size
  Make sure you choose a robot lawn mower that can handle the size of your backyard. We’ve tested models for a range of areas up to 2,000m².

• Slopes
  The robot lawn mowers we’ve reviewed were tested on slopes of 19° (35%). Some performed better than the manufacturers’ claims. Some models in our test are claimed to handle much steeper slopes too – up to 39° (80%).

NOTE: The user manuals of certain models state the mower should only be run on the maximum claimed slope for short spells – the whole mowing area shouldn’t be at such a slope.

• Mowing zones
  Check that the robot mower you’re considering can handle the number of mowing zones you want it to manage. Some models we’ve tested can only mow a single zone, while others can handle up to 20.

• Cutting heights
  Most of the mowers we’ve tested can cut as short as 20cm, but some can only cut down to 30cm. Most have a 30cm range with at least 4 cutting heights, but some have less. The best robot lawn mowers we’ve tested have a 40cm or 45cm range with 9+ cutting heights.

Navigation and guidance systems

• GPS-assisted navigation
  Robot mowers with this feature use GPS to track their location. This means they know where they’ve already mowed. This prevents unnecessary overlap. Good satellite coverage is required, with a clear view of the sky.

• Real-time kinematic (RTK)
  Models with RTK have more precise (centimetre-accurate) satellite-based positioning. This means the mower accurately navigates your lawn and around no-mow zones, cutting your grass and not your flower-beds. The RTK antenna usually needs to be installed on the roof of your house or shed for the best line of sight to satellites.

• Algorithm-based navigation
  Many robot lawn mowers move randomly within a set perimeter. But robot mowers with algorithm-based navigation use GPS, sensors and/or cameras to map the lawn and track their position. They follow software rules to mow via efficient routes and avoid obstacles.

• AI-assisted navigation
  Robot lawn mowers navigating with AI assistance use cameras, GPS and various sensors to learn the layout of your lawn and map the best mowing route. They can adapt as conditions change. They also use AI assistance to detect and avoid objects like trees, flower-beds, people and animals (see Vision).

• Vision or AI Vision
  This is a system that uses cameras and AI to recognise common garden objects. Some robot lawn mowers that don’t have full AI-assisted navigation have AI Vision.

• Light detection and ranging (LiDAR)
  Robot lawn mowers using LiDAR bounce laser light off objects to build a 3D map of an area to plan mowing paths and detect obstacles. LiDAR can contribute to AI-assisted navigation but it’s also a stand-alone feature of some models that don’t have AI.

Control and connectivity

• App for Android and/or iOS
  Some apps only work with Android or iOS. Check compatibility with your phone’s operating system if you’re considering buying a robot lawn mower. All the robot lawn mowers we’ve tested have an app that’s compatible with both Android and iOS.

• Voice assistance
  This feature lets you control certain aspects of the robot by voice, with the help of Google, Apple Siri or Amazon Alexa. If you want to use this feature, make sure the robot lawn mower you’re considering works with the voice assistant on your phone.

Weather features

• Rain sensor
  A robot lawn mower with a rain sensor will return to its base station when it detects rain. It will resume mowing when the weather clears. While the models we’ve tested are water resistant, lawn mowers usually cut better in dry conditions. Fewer than half the models we’ve tested have a rain sensor – even those with the lowest damp grass cutting scores in our test. Check our test results before you buy.

• Ingress protection (IP) rating
  This tells you how well a device resists dust/solids (the first number) and water (the second number). The higher the number, the greater the protection – so IPX6 rated robot mowers have better water resistance than IPX5 rated models. (An X means the device wasn’t tested for resistance to dust/solids).

Other features

• Anti-theft features
  Robot mowers usually have a PIN lock and alarm. Some sound a warning tone and send an alert to the mower’s app if they’re lifted from the ground. Certain models will alert you via the app if the mower moves outside its virtual boundary (commonly referred to as a geofence). And some have GPS theft tracking.

• User-replaceable battery
  When choosing a robot mower, make sure you can replace the battery yourself – it might cost you more if you have to take the mower to a service agent. Also check you can get the batteries locally and what they cost.

Check out our robot lawn mowers reviews to see which models have the features you want.