At some point, a military device / weapons system recognises that it's not operating to spec and either disables itself or diverts and destroys itself in a non-target region.

Keep in mind that for most weapons, not activating when not specified is far more useful than failing to activate where and when specified. See the case of several "broken arrow" nuclear weapons incidents in which failsafes prevented unintended detonation. In once case with only a single fail-safe preventing that detonation which would have been in a civilian populated region of the United States.