It seems odd that the designers of such a potentially life-critical device would choose a method with such potential for accidental triggering for such a functi

It seems odd that the designers of such a potentially life-critical device would choose a method with such potential for accidental triggering for such a function. I guess it's a tradeoff between likelihood of accidental triggering vs not having the capability to disable it in a genuine emergency due to lack of equipment. Then again, if your paramedics/hospital don't immediately have a (strong enough) magnet on hand, you're no better off than them not having the special disabling-device. I guess magnets are cheaper, and don't require batteries, but is that a sufficient reason to use such a signal? Even something like requiring a varying magnetic field at some fixed frequency (and of a high enough power to not trigger on RF/spurious EM) would be much less likely to accidentally trigger, and the disable-device could be an electromagnet driven by an oscillator. Any other ideas why this method might have been chosen?