I have a metal box with overlap and metal taped edges that my vehicle still detects the fob thru. The chip signal amplifiers are pretty strong. For improved security I took the battery out of the fob and now the chip has to be within a half inch of the start button.
Chirp has been instrumental in helping “unlock” certain GMRS radios that come from the factory locked down to satisfy FCC requirements. The Baofeng UV-5X(G) comes to mind
i have some from Nest that claims to be military grade. Big enough to hold a HT with antenna. These are more designed for EMT protection with i would think would work against cell phone detection.
1) NO
2) You would be able to transmit on non-GMRS frequencies but still have the convenience of having the pre-programmed simplex and repeater channels.
Did that actually stop the people who were not authorized to use it?
I would think most interfering users would figure out what the new tones / codes were pretty easily, unless they just got the tones and had no idea they were not authorized.
Which is BS. If we were trying to do anything 100% on our own we'd still be living in caves eating whatever grew on the land and whatever squirrel we could manage to hit with a rock.