What device should I use to control my magnetic door lock

Ah yeah that might be a problem. The issue won’t be the lock not getting the correct amount of current, the issue will be that the implant will have to handle the full 500mA, which could cause its relay (or whatever it uses to switch) to burn out. You could add an additional stage with a bulkier relay that can handle the 500mA (and which would be switched by the implant).