Aren't there situations where this could backfire? What if you just finished running around the block and need to get inside? What if you just finished running around the block away from rabid dogs and need to get inside FAST?
Perhaps this wouldn't be a good choice for a front door to a regular home. Perhaps the entrance to a secure facility, though, where time would never be an issue (with a keycard and a vocalized passphrase as well, for additional factors.) Not a nuclear launch silo, but perhaps a top-secret research facility.
