How does vacuum cleaner "Searching the house"

How does the vacuum cleaner find where to go for charging, what sensors does it use for this? Of course, we are not talking about any GPS, it simply does not catch in the apartment (reinforcement and other interference). Maybe inertial sensors, just calculating how many meters he traveled from home by the number of wheel rotations. But then he would not find the house when I moved him from one room to another. Vacuum cleaner robots have infrared photodiodes to determine the distance (there are many more different sensors).

So, these sensors count the time from the emission of a beam to its reflection from the surface towards the sensor receiving the reflected light (this is how the distance is calculated). And while searching for a house, the robot looks for the rays that the house emits (radiators of infrared light are built into the station). The robot begins to spin around the axis, trying to find the glow of the house with the help of photodiodes. And given that there are two bulbs, they allow the robot to precisely park opposite the glow (in general, it looks like a snake spell).