Would you rather lose Electricity or Water for your life?
I have seen one sold at auction I believe it sold for about 300 dollars.
closer to the ground, less weight..
Most smoke detector is battery powered to avoid line electric failure and lost its detection function. The code requires this device either has its own battery power source ( rechargeable mostly ) or link it to both normal AC power line and an emergency power generator power source ( no need battery in this device) , if hundred of these devices are installed in a large commercial building.
