Hi @gth, 'marker' is from the origin of the things when they were originally used to throw a paint pellet at a cow and mark it. America!
In Australia there are so many people who are rabidly anti-everything that it's common to continue referring to them as markers and disassociate them from actual guns. There's a lot of backstory there, and only recently being allowed to have some things at all, like the Tippmann A5 which is still illegal in some states I believe.
My antique one is illegal in Victoria because it has 'the same profile as a longarm' because the magazine runs alongside the barrel instead of being a clip on hopper.
On that subject, the reaction when I presented the A5 to be registered at the local police station was exactly that. The female hossifer actually backed away, saying Wtf a lot. It was all a little bit emotional. This because legally I must state my intention, 'officer, I have a firearm in this bag to be registered, may I place it on the bench and open the bag for you?' at which point she is expecting a gun, not a marker and mistakenly sees an MP5 instead of an A5.
Anyhow, it would need to be fail_lock to be a workable solution for a firearm, otherwise just popping the battery would be enough to bypass it. I'm thinking of something along the lines of a pin that jams the mechanism the someway most safety mechanisms work. Then removal of that for a period when the firearm is held by an authorised ring wearer.
It would mean that the battery would run down fairly quick and that any issues with the mechanism would render the firearm inoperative until it was repaired, bur I think that's the only realistic way to do it.