Post image unsplash-logo Tommy Kwak

Most owners of robotic lawn mowers should be familiar with “islands”, a commonly used term for areas where you don’t want your mower to operate. In this post I’ll share some insight and compare two methods for creating such islands - traditional perimeter wire loops and magnetic strips. They may look similar on paper but are quite different, both with their pros and cons.

This post contains my own thoughts, observations and opinions and is not sponsored or endorsed by Worx. All observations are from a Landroid WR155E with firwmare version 3.26.

Perimeter wire bouncing

Before going into details about islands I’ll just briefly cover the basics of the perimeter (or boundary) wire.

The perimeter wire acts like a virtual fence, pegged down all around your lawn, creating a boundary for the Landroid to operate in. The wire is connected to the base station that generates a signal with a specific frequency. The Landroid then uses a very clever mechanic called tank circuit, calibrated to the frequency of the wire, to make sure it stays inside the boundary. The combination of the signal wire and tank circuit allows the Landroid to quite accurately detect when it closes in on the wire and also follow along the wire if necessary (for example when returning to base or when moving between zones).

AIA intelligent navigation

As your Landroid moves around your lawn and eventually hits the perimeter wire it will stop and turn around, “bouncing back” into your lawn. (much like the balls hitting obstacles in the classic 1970s arcade breakout games)

Some manufacturers use a random turning pattern, meaning the robot bounces back from the perimeter wire in any valid direction. Worx have something called AIA intelligent navigation. It sounds advanced but it really just limits the Landroid turning pattern to a forward facing 90 degree area. In other words, your Landroid never turns completely around when hitting the wire (with regards to the wire’s orientation). This makes it easier for the Landroid to push forward through small corridors and (supposedly) covers more of your lawn in a shorter time.

Bouncing Perimeter wire in black, with an island (yellow). Random bouncing behaviour (left) vs Worx AIA navigation (right).

Perimeter wire islands

As you lay down the perimeter wire, you’ll probably loop in at least a couple of islands - areas where you don’t want the Landroid to be. This can be things like pools, flowerbeds, loose sand, gravel, etc. The reverse signals from the “bridge” wires (the two cables to and from the island in the picture above) will scramble each other out enough to not trigger the tank circuit, making sure the Landroid can pass safely over it. Pretty clever!

This method is straight forward as it’s a built in functionality of the Landroid and doesn’t require any extra accessories, just some more wire and pegs. Also, the AIA intelligent navigation pattern will be used whenever the Landroid bounces off the island wires.

But these types of islands also have some drawbacks. First, as Landroid owners know, it takes time to cut up, extend and peg down or bury the wire. It also has to be a complete loop and go back to the perimeter right next to the outgoing wire. Secondly, these types of islands are limited in size. The wire length of the island cannot exceed 25 meters, or the Landroid will confuse it with the yard boundary and get stuck on it when returning to charge. Thirdly, when the Landroid has low battery and returns home or changes zone, hitting an island like this will cause the Landroid to crawl around it one and a half lap. This not only takes up time but can lead to visible wire tracks if the island has sensitive areas like loose soil or sand.

Off-limits sensor

Worx offer the off-limits accessory, which is a sensor you plug into your Landroid that enables it to detect magnetic fields. It comes with a roll of magnetic cable that you can cut up and place freely, acting like a virtual fence just like the perimeter wire.

The main idea with the magnetic strips is that they are much easier to place. Instead of planning for (and possibly cutting up) an existing perimeter wire to create a loop you can just cut off piece of magnetic wire and place it in any shape and length on the grass. This is great for quick and temporary no-go zones, but pegging or digging down the magnetic strip you can also create more permanent islands.

Magnetic strip islands don’t have the limitations of perimeter wire islands. They are not connected to the existing perimeter wire and they can have any shape and length. You don’t have to place it in an enclosed loop, but can cut it up into whatever shape you need, like straight lines, arcs, etc. This gives much more freedom and allows covering up more complex areas. The kit also comes with a couple of connectors that can be used to extend the total length by connecting multiple magnetic strips.

The two most noteable drawbacks of the off-limits sensor and its magnetic strips are the price tag and the very basic reaction from the Landroid when it encounters a magnetic strip. It stops, backs up a bit, and then turns a complete 180 degree around before continuing. That’s right, it always turns 180 degrees - nothing random, no AIA intelligent navigation pattern. This means if you are dependant on the AIA navigation pattern (to push through small corridors for example), magnetic strips are probably not what you want in those areas. In fact, instead of keeping the forward momentum as with AIA, magnetic strips always reverse the momentum, as described in the picture below.

Magnetic bouncing Bouncing on a magnetic strip island (red line) is always 180 degrees. Combined with perimeter wire/AIA (black line) this always completely reverses the Landroid’s momentum.

On the other hand, the aforementioned perimeter crawl does not happen with magnetic strip islands. So they are useful for more sensitive areas where you just want the landroid to bounce back and not (potentially) spend time circling around the island.

The off-limits accessory also enables shortcuts to be placed on your perimeter wire, to speed up the Landroid’s route back to the charging station. I’m not going to cover it in this post but it is a nice bonus feature that you can read about on Worx help pages.


The off-limits sensor is quite versatile. I initially got it for the shortcut feature alone (which, on my fairly complex lawn, saves up to 20 minutes every time the Landroid returns to charge!), but I also had a perimeter wire island I wasn’t happy with and couldn’t get to work consistently. It was either too large, caused visible wheel tracks or the Landroid getting stuck. This was neatly solved with a magnetic strip island. I also throw out pre-cut magnetic loops now, instead of turning off the Landroid or placing down planks, when I sow new grass, dig holes or play Kubb.

Both the off-limits sensor and the magnetic strips have hefty price tags but it allows very quick and simple no-go zones and can help with certain complex island mechanics. And the shortcut feature alone (although a bit hit-and-miss sometimes) is awesome for large lawns.