Power over Ethernet (PoE) is a standard that carries both data and low-voltage electrical power along a single Ethernet cable. A device such as a Wi-Fi access point, IP camera, people counter or VoIP phone can be powered and connected through one cable.
Power is supplied by a PoE-capable network switch or a small injector placed in the cable run. Common standards, such as 802.3af, 802.3at and 802.3bt, deliver different amounts of power, so the switch must supply at least what each device needs, and the total across all ports is limited by the switch's power budget.
It is popular in stores and venues because ceiling-mounted devices do not need a power point nearby, which cuts installation cost and clutter. A single battery backup (UPS) at the comms cabinet can also keep PoE devices running during a short power cut. Venues adding people counters, cameras or digital signage later often find PoE ports already available, which keeps future upgrades quick and tidy.
Check the power budget, the standard each device needs, cable quality and length (generally up to 100 metres), and compatibility between brands. Cheap or undersized cabling can cause overheating and unstable devices.
PoE simplifies installation and improves resilience, but it should be planned with the rest of the cabling and switch layout.