S.O.S. pendant is not a tracking device !
I always put my SOS pendent on every morning, I take a blood thinning drug that would figure if I were in a similar predicament to your husband Floo, I got my one on line, I did get an opportunity to ask an ambulance driver about it and he said they are completely familiar with them.
The pendent is waterproof it unscrews and there's a small paper concertinaed into it that has plenty of room for any info you need about the carrier, I've just measured mine it has a 22 mm diameter and it's 4 mm thick, stainless steel with S O S stamped on it in bold lettering.
Can't remember how much it was I've had one for years, (you can get one with a cross on it
), hope this is a help for you Floo.
Kind regards ippy