I have a laser torch (one that comes as a key tag).
is there anyway to do something useful with this?
like obstecle sensor?
If it has to be simple, you could use it as a broken beam detector by shining it on an LDR.
For an obstacle detector, you need to modulate the beam and use a photo transistor with an amplifier with eg. a PLL tone detector (like NE567/XR567) that sense when the beam lights up an object. It will be more involved and ambient light might be a problem if used outdoors.