Originally Posted by shakran

there's more than one way to turn something off. the Xponder may not have an actual off switch, per se, but it will have a breaker/fuse on its power wire. that's pretty necessary becasue it would suck if something went wrong with the transponder and the airplane burned up because it wasn't fused

Additionally, you don't necessarilly have to turn it off. Just flip it to a different setting. If air traffic control is looking for your transponder at 1600, and you flip it to 0900, they won't know who or where you are.