Jack, probably around 2001 we were experimenting with a modified SARBE. Dedicated frequencies away from the Emergency ones. These were coded and would burst transmit a GPS location over UHF. This could be picked up on the SARFIND box which listed the loads and locations. Just march with your hand held garmin and there it was.
Probably overcomplex for a harness pack but the requirements fell out of loosing a high value load on an overseas exercise (Safe Saria)
All the kit was disposed of to the School at St Mawgan to one of the Squipper WOs
remember trialing various lights including some IR which would flash a code. Mocking Bird they were called and could be programmmed. The change from IR to white light was effected by putting the batteries in the other way round. Like most things of this nature they were pilfered. Apparently they were useful to the Scuba divers.
Not sure what became of the pingers we put on boat airdrop platforms. Again that came about through having lost one.