A beacon is usually a light source,  in a rotating enclosure blocking emission in one direction and a window on another direction.  Think of a police vehicle beacon.

 

What other 'emissions' can be/are used instead of light ?   As sound as Leslie effect, radiowaves,   magnetism ?  gamma rays ?    that can be detected at -say 50- metres away ?

Nowadays when I hear “beacon” I think of Bluetooth. https://en.m.wikipedia.org/wiki/Bluetooth_low_energy_beacon

If you want to get directional information you would need several so you can triangulate. 

Radio and Sonar ones are out there, commonly in use.

Also wifi beacons: Wi-Fi challenges Bluetooth for the beacon market | Computerworld:  https://www.computerworld.com/article/2975859/mobile-apps/wi-fi-challenges-bluetooth-for-the-beacon-market.html

 

On 8/20/2018 at 2:41 PM, Endy0816 said:

Radio and Sonar ones are out there, commonly in use.

Ultrasound scan can be directional.

Some sonars are directional, especially for seabed mapping, and need a very wide base. Helicopter sonars are little directional because the size is few wavelengths, but submarines may have transducers over all their length.

Seen them used for navigation. Like underwater lighthouses.

The submarine locator(placed on when testing) works along the same lines.

https://en.m.wikipedia.org/wiki/Electric_beacon#Sonar_beacon

I think all they do is transmit. Not sure.