You can get cheap wifi video camera on ebay, $20http://www.ebay.com/itm/Wireless-WIFI-H ... 2169728634
This camera needs 5V input.
Existing wiring for American doorbells has a 12V AC transformer in series to a switch and then the doorbell. It is also allowable to leak several watts (for a lighted doorbell button) without making the chime ring.
So what kind of circuit is needed to:
1) make 5V from the several watts you can draw without triggering the chime
2) provide a way to close the circuit (TRIAC?) so that chime can have full current and sound
3) Keep making 5V for the camera while chime is sounding (pulse the TRAIC?)
Can this be hacked together with something like a 555 and a TRIAC so that the camera always gets 5V and then has a GPIO to sound the chime?