Power over Ethernet. See the discussion of PoE on the FAQ page. Power over Ethernet uses the 4 spare wires in Cat5 cable to supply power to devices with Ethernet connectos, or to "splitters" or "injectors". Video surveliance equipment often yses PoE. Those enabled with pan-tilt control can get their power and control commands and send video, all over a single Cat5 Ethernet cable.
DIY PoE is PoE that does not conform to the standards and is also much simpler. You supply power, like 12 or 24 volts DC amd do what you need. It is a good idea to use a brige rectifier at each delivery point in case anyone swaps wires around. This uRata device, http://search.digikey.com/us/en/products/OKI-78SR-5%2F1.5-W36-C/811-2196-5-ND/2259781 available from DigiKey, takes 7 to 37 volts DC and delivers an amp at 5V or 3.3V depending on versions. They look a little big in the pictures, but are truly the size of a TO-220 device. Very cool and we use them here at ARMWorks.
Our Injectors and Splitter can work with Standard PoE equipment or DIY. Mixing the two is not recomended.
PoE 24Volt: 1250 mA power supply with power cord and dual RJ45 jacks. POE24VP
PoE 24V outlet mount: 24V wall mount/power socket mount type. POE24VW
PoE 12V outlet mount: 12V 1000 mA wall mount/power socket mount type. POE12VW
PoE Injector/Splitter Pair 5.5x2.5mm: A set of one inject and one splitter for adding PoE to any Cat5 cable. POEIS25
PoE Injector/Splitter Pair 5.5x2.1mm: A set of one inject and one splitter for adding PoE to any Cat5 cable. POEIS21
PoE Mounted Injector: A small plastic PoE injector with mounting ears. POEMI