A radio station that broadcasts a directional signal for navigational purposes

A tower with a light that gives warning of shoals to passing ships

The typical beacon is a brightly painted tower, perhaps manned with a pyre and bell. Manned beacons are expensive to operate and tend to be limited to larger ports. Only major ports keep them burning all night; vessels normally enter/leave a port during daylight hours, unless it would be dangerous to wait outside the harbour. Some ports have buoys marking submarine hazards outside the harbour.

A wireless LAN packet that signals the availability and presence of the wireless device.