The two laser modules, which are 2 inches long and 1/2 inch dismater (certainly less that that) run off a 5 volt supply. You can get tham fitted with lenses to give amore focused output. I got mine from Maplin (UK firm) at £10 each. The dtectors are three wire Schmidt trigger devices, giving an instantaneous change fro 5 to 0 v if hit by a laser beam. They drive TTL and CMOS directly.
I have my lasers mounted on the table shining onto detectors mounted on the lathe body. There is no physical contact between the two, indeed, they with work over a long distance if required.
Excellent, repeatable results, to less than 2/100ths of a mm.