[Question] Is the player detector auto - checking the area or do you have to click it?

Hey, in Direwolf20's SMP i saw the player detector and he right clicks onto a player detector to open a force field.
In another topic i saw an auto - "logged in" - program, so my question is if the player detector is able to check the nearby area for players.
Hope to get answers soon,
sincerely,
Skampi. :)/>

As far as I know, player detectors need input (usually by right clicking), but there are probably some mods out there that use chunkloaders or MFFS items or such, connected to computers, to identify players.

This is mostly guesswork from my part, so I'm sorry if I'm way off.