Haven't done any extensive testing, however when I placed a light barrier on my base earlier, set the 'front' setting to 2...when I opened the control panel again, it reset to 1. and every time thereafter. it was placed over a teleporter, such that at a length of 2 it will detect a player on the teleporter.
I have no clue about the light barrier, but a normal motion sensor works for the task you want to be done.
requires you to leave the teleporter and step back on it, if you just teleported in. i've been using the motion sensors, but I wanted to get around that quirk.
I found when the light barrier is set to =< 4 the distance gets reset but => 5 it doesn't. This will be looked into.
