In these projects we take our standard circuit and customize according to our customer preference.

Power fail alarm with ultra loud buzzer
This is used for a burglar alarm.  If the power gets cut to the house, this alarm mounted up high will alert neighbors to call the police, and probably scare away the burglar. THE VOLUME (SPL) of the siren is 118 dB at 2 feet!  This is painfully loud if you are the same room.
It is mounted in a weatherproof enclosure 6 x6 x3″.  There is an auxilliary input for a secret silence switch. (unknown the to buglar)