One of the best apps that a firearms owner should have on their phone is called CCW (on Google or Apple.) It is an app that shows all laws and statutes for every state, including reciprocity laws, prohibited areas and other things of that nature. It is constantly updated. It shows easy to digest information that if you click on will go to the actual statute. There's no excuse for not being informed of the laws if you carry.
There are these type of devices, but I'm not sure if you have already considered these, and to be honest a reasonable cable cutter would make short work of them.
FWIW: https://www.amazon.com/SuperDi-Toolbox-Cabinet-Security-Finland/dp/B079237PSD/
About the same price as a tubular keyed one, and far less likely to be susceptible to anything as simple as the old Kryptonite/Bic pen hack.