Batteries from China are not that great, so you can get batteries from here.  

A very simple device, current from a 9v battery makes contact with water and sets of a siren.

For keypads locks you have basically 3 types, mechanical, battery, and internet capable.

And some areas require that the detectors (smoke and CO) be hard-wired (to AC power) AND have battery back-up (which all AC powered units I've seen already have).Become familiar with your local building codes and inspectors.

We used a battery powered sawzall type tool to cut out our one piece tub and there was no sheetrock behind it.

If you have wifi, then the best no hassle cameras are battery operated ones.

For example, I have a "Section 8" bucket with things that are typically needed for Section 8 inspections: 9V batteries; clear packing tape, extra outlets, window locks, outlet and switch covers, etc.

Well there are plenty of shared economy applications that allow you to earn extra cash off that battery powered ego machine(s).Really though, what if you tried to make a car sharing service into a investment model?

It should come with two batteries and a charger.

I've seen fake alarm systems which basically are stickers, SIGNS "(This Property is Under Video Surveillance" etc), and even flashing red lights that are battery powered-battery powered alarms - they have these at harbor freight, you can put on windows and doors- they're powered by magnets --Does anyone have recommendations for better battery powered or simple DIY alarm systems?