Robotic lawn mowers represente the second largest category of household autonomous robots used by the end of 2005. A typical robotic lawn mower requires the user to set up a border wire around the lawn that defines the area to be mowed. The robot uses this wire to locate the boundary of the area to be trimmed and in some cases to locate a recharging dock. Robotic mowers are capable of maintaining up to 5 acres of grass. Power usage varies from about 100 watts (comparable to a light bulb) for 1/2 acre to 500 watts (comparable to a refrigerator) to maintain 5 acres.[dubious – discuss]