How do (In room) hotel smoke alarms work and differ from home units? And does it differ between age and types of motels such as Best Western vs an off brand in your town for only 80$ a night? Also who keeps maintaining them? Is it possible for a guest to PUT IN a Lithium battery if they discover one missing (either at their own expense or perhaps take it off the room bill later) after notifying the front desk they made the non working alarm now suddenly working and prove it to them?