I discovered a technique for locating ELTs in locked hangars. I stuck my radio rubber duck antenna in the crack of the door so it got partially inside. The signal either went up, if it was there, or disappeared because the metal door was shielding it from the source in another hangar. This probably only works for hangars that have horizontal sliding doors. For vertical lift doors, you would have to poke a longer antenna through the seal on the bottom of the door. As usual, using signal strength approach, remember to keep tuning the receiver either up or down to keep the signal level a little scratchy. I was already at 121.75 and still getting a strong signal when I poked it in the hangar.
I've had luck taking the rubber duck antenna off of the handheld and then touching the antenna socket of the handheld against the metal door (or airframe if trying to isolate an aircraft on the ramp).