Ok, now that almost everything that was to be said has been re: laser
safety, I'd like to meekly add that I've been there and that normal IR
lasers used in CD pickups, used without any kind of lens, will give
hardly credible ranges in combination with SHARP GP1-XXX remote control
detectors and 40 kHz modulation. 20 meters is very easy, provided you have
a steady hand (as in shooting ;). The cost issue, however...

I have modified a TV remote control for someone who has a large screen
projection unit in the ceiling of a pub in this way and it works OK, but
if you do this yourselves, use a limiting R and reverse current protection
diode on the laser including while manipulating it.

I do not know if the diode I used in the remote control is lasing or just
leding but viewing with an IR BW camera shows characteristic laser
patterning (stars). The input power is too low to do any harm, besides not
being continuous. It is a 'class 2 laser product' I think, with 1-2 mW of
beam power.

sorry, I could not resist this.

Peter