someone else mentioned it, but don't rely on this to find a crashed airplane. any airplane crasher worth their salt will splatter parts over at least 30 feet, you may not even FIND the battery pack! but again, they are great for reminding you to turn off your plane, the cost of this alone could be made up with one destroyed pack if you left the plane on once... also, i've lost some fairly pricy coreless servos to a plane that I left on once. apparently when it got low the control surfaces started twitching, and eventually burnt out the coreless servo motors.