I had an idea attacking the problem from a different angle: a two parts device, one attaches to the owner's belt and the other attached to the equipment, the two communicate wirelessly to estimate the distance between them, and if it crosses a settable distance, both emit an alarming sound.
This can protect against equipment being stolen or forgotten, and can be used for other purposes, e.g. childs getting lost in a crowd. It would be easy to attach to a camera using a miniature version of bike locks on the loops holding the neck strap, but lenses are a different story.
I've consulted a knowledgeable businessman I trust, and he says this idea can't be protected by a patent, so developing it is a problem - if it succeeds, it will be immediately copied, making it unprofitable.