Pit droids, or DUM units, are preprogrammed workers, which are mass-produced on a planet named Cyrillia. They are nearly four feet tall and can lift items several times their weight. They are usually sent to planets in which the dangerous sport Pod racing is allowed. The pods, even when not moving, are very dangerous, and pit droids are the most inexpensive way out of fixing them. Then when not in use the only thing which one must do, to turn it off, is to hit the large button on it saucer shaped head.
Pit droids being unstable and unreliable, even in a totally repaired state, can never be left alone with anything without the droid or the item being in danger of becoming broken. In many cases a pit droids can malfunction and, with its strength, become hazardous and destroy anything it can find. In some really bad situations the on/off switch on the droid is damaged when the droid becomes malfunctioned, causing many pit droid owners to carry ion blasters with them, just in case.
Based on the information from: www.starwars.com