Cool solution to show the status of door lock is given by Martin Howell. He uses a standard micro switch, mounted on to an aluminium plate which is screwed to the inside of the opening in the door frame where the lock tongue goes in, two LED lights and CAT5 wiring for each switch. The wires come from the ‘engine room’ where server and all network stuff are located and carrier power from a central 12v power supply to the LEDs. Using CAT5 he receives the status of each lock to the central place. It’s passed to the HomeSeer server via Ocelot. As result the status of the door lock can be viewed from touchscreen panel or system will say about it via SONOS players using text-to-speech software.
Simple and cheap solution but it’ll help you to make your house more secure. Sure such approach can be used for new house with more then one door (my friend has three plus garage). There is a possibility to install door/window sensors but they can indicate open the door or window or not. The status of the lock is unknown in that case. You can use “smart” locks such Schlage LiNK but it’s too expensive than the Martin’s solution.