Re: Old timer doubleplus good...
"a key fob that doesn't respond to a challenge/response call unless an accelerometer within it detects the fob is moving"
Attempting to solve an unnecessary problem with another layer of complexity? Complexity and security are in inverse proportion -- always.
Modern mechanical locks are can be very secure. The problem is that a decent mechanical lock and key cost a lot more to make and install than a plastic dongle and a solenoid backed by a bit of code.