The simple combination of a small child playing on the grass and a robot lawnmower doing its job can end in horror, consumer protection experts say.

If a toddler's arm, hand or fingers end up in the way of a robot lawnmower, then he or she is more than likely to be severely injured, according to recent tests of eight different models of smart mowers on the market.

German consumer protection organisation Stiftung Warentest found that almost all of the eight tested devices sliced into the fake child arm they put on the lawn during tests.

For test results published in March, the product testers simulated various situations on the lawn in which children could get too close to these autonomously driving garden gadgets.

Fortunately, a dummy of a crawling child's foot managed to escape the robotic mowers unscathed.

The testers also criticised the way in which some of the devices were programmed to turn off in emergencies. All robotic lawnmowers have a red stop button which anyone can push when something goes wrong.

The testers argued that if this is pressed, the device should remain switched off until it is restarted manually. Two robots did not do this, however, and simply started up again after a set pause time. One model restarted on its own after shutting itself off when being lifted up.

Robotic mowers are still a relatively new segment of gardening equipment, which is why the product testers are still finding problems beyond essential safety issues.

Some robots can't handle wet grass or take forever to get the lawn properly mowed. Others rarely manage to cut the grass in corners and even get stuck sometimes.

And if your garden has a slope, then you may want to think twice before getting a mower, Stiftung Warentest testers say. According to their analysis, almost none of the tested robots worked smoothly on slopes.

Like robot vacuum cleaners, mowing robots are designed to use sensors to automatically detect any obstacles and mow either randomly or in systematic rows. Some models can be controlled with a smartphone and stop mowing automatically in the rain.

Some gardening experts argue that through permanent cutting and mulching, they can achieve good results mowing the lawn, with the fine cuttings serving to fertilise the lawn, which thus becomes denser and more resistant in the long term.

For those with small and exposed urban gardens, however, the digital technology is not quite as attractive as for people with suburban or rural lawns.

For a start, there is a risk of theft, particularly with such expensive devices. Digital mowers tend to cost upwards of US$500 .

 - dpa