hi,
I'm using it in a barn, so I guess it's a mix of indoors and outdoors? What's the difference between visible and infrared laser if I just want to see if the laser reception gets intercepted?
If visible is acceptable, then you could use a low cost laser 'pointer' device.
If ambient light was going to a problem, you could use a 38KHz infra red system.
What objects and over what distance to you want to detect a 'blocking' object and what action do want the detecting electronics to take?