I carry a white Photo II on my keyring. It's on a short lanyard (don't remember if it's a Photon lanyard, or from a Mag Solitaire), and connected to the ring via a deadlock quick-detach connector, so I can remove it when needed.

The short lanyard lets me actually illuminate a keyhole without detaching it, and keeps it below the rest of the stuff on the ring.

I, too, experienced problems with an early Photon III, but LRI replaced it without question. On numerous occasions, I removed it from my pocket to find it already on. I figured that things in the pocket (largely keys) were pressing the rear half of the switch & turning it on. With the PI & PII, even if they do get "bumped" in your pocket, when the pressure is relieved, the light goes off--not so with the PIII. It's now relegated to nightstand duty.

I went through several sets of batteries with the PIII, before figuring out the problem. However, I've not had the same problem with the PII, which is why I carry it.

Prior to the Photon, I wouldn't put any light on my keyring. Over the years, I carried most of what was available in quality small lights, starting with a 2-AA Tekna dive light, & progressing through the various Mini-Maglites (AAA & AA, & Solitaire). I was most satisfied with Pelican's 2-AAA MityLite. I have about 4 of them, & they're fabulous. I also had good luck with some Underwater Kinetics 2-AAA. Everything I mentioned, though, was too big to put on a keyring.

Now, the Photon is always on my keys, and a SureFire 6P is usually on my hip.

David