There was a programme on French TV about a Swiss avalanche burial on the French side of Mont Blanc. The victim was deeply buried and the avalanche dogs could not locate him. The PGHM (French Mountain Police) said they would have to wait for spring to recover the body. The family hired a ground penetrating radar and the operator and brothers/friends of the victim spend two days searching the site. The radar had to be dragged on a sledge. Eventually they located the body. The PGHM were extremely dubious at the start but very admirative of the family and their efforts at the end of the documentary. GPR units, as used by archeologists, are much smaller now than 5-10 years ago (when the programme was made) and maybe they will see more use in the future.
This season the French PGHM are experimenting with radio location of mobile phone signals.
http://pistehors.com/news/ski/comments/0985-spooks-gadget-could-revolutionize-mountain-rescue/
Mobile phones etc can also be picked up by Recco units which have made considerable progress in the last few years with some live recoveries here in the French alpes amongst others.
I’ve experimented with RFID location a couple of years ago. I can post the results, which are quite promising, if anyone is interested?
Of course some of the gadgets are more in the bizarre end of the spectrum, such as the DKL Lifeguard
http://pistehors.com/news/ski/comments/les-gendarmes-renifleurs/
You may remember a similar device was sold in big numbers to the Iraqi govt. to detect suicide bombers.