Abstract: A device to be lowered into a string of well drilling pipe to the location of a non-magnetic section of the pipe near its lower end, with the device including a compass assembly or other instrument for making a photograph or other record at that location. The device includes a detector which responds to arrival of the device within the non-magnetic section of the drill pipe to automatically energize the instrument for making the photograph or other record. The present invention provides a test circuit for this type of device enabling it to be quickly and easily checked at the surface of the earth before being lowered into the drill string to make certain both that the detector which responds to arrival of the device in the non-magnetic section of pipe is in working condition and that the batteries which energize the device are at a sufficiently high voltage level to assure effective operation of the device in the well.