One output works with the Basic Stamp, the other output works with the Basic Atom Pro. I forgot which one works with which MCU. It’s been a while since I messed with this, but trying both will tell you which one works. I believe the one connected to R4 is for the BAP and the other one is for the BS2. I remember the Stamp worked inverted to the BAP’s adin pins. Also, changing C1 to a higher value will change the delay that the LED stays on, and the pot will adjust the sensitivity. You could try using a 10uF trimmer cap and really tweak the way you want it to work.
I forgot to add to the schematic that Q1 can be a 2N2222 switching transistor.