A battery-powered blade cuts the grass in a random pattern within a boundary defined by a buried cable; $700–$4,000. Shown: Robomow RM200, $1,300; friendlyrobotics.comPros:
Programmable; works on any day you want; recharges itself when low; stops cutting if it rains
or the grass is wet; quiet. Cons:
Expensive; has only an 8-inch cutting width, so it can take a while to finish the yard.