These are too obvious - 5-15 minutes gives your victim way too many opportunities to narrow down the location. What you really need is one that chirps once eve

These are too obvious - 5-15 minutes gives your victim way too many opportunities to narrow down the location. What you really need is one that chirps once every (multiple of) 20-28 hours (with weighting towards 23-25 to keep it roughly around the time you set it going and an infrequent skipping of a day.) Also with different volumes and, ideally, different chirps. Occasionally a double chirp just for extra insanity causing. (A Michael Jackson "hee heee" would be another good option.)