Isn't Android 4.x now EOL? Why even try and code apps for that generation of droids? If the (l)user really want IoT Yale keys, then surely said (l)user will be happy to shell out £££ (or $$$) for a new Android device running 6.x (or higher) as part of the requirements.
Three words : lowest common denominator.
If, by using an old Android version they unwittingly causes grief for themselves, then it's their own fault for doing so.