English: Automatic robotic lawn mower Gardena Sileno City 250 (model also known or renamed as Minimo) in action. The mower is basically a model from Husqvarna sold under the Gardena brand. During parts of the video, a black thin line can be seen which extends straight across the garden area. This is a part of the "orientation" or guidance lines which have to be installed prior to first operation of the mower. They extend mainly at the physical outer borders of the lawn (e.g. in front of the bushes in the back), so that the robot can calculate where to turn around. The cables carry very weak electrical alternating current (or pulsed) signals (voltage unknown to the author, but probably not more than about 15 Volts), which are received by the robot via an antenna when approaching the lawn border.