Bad hit detection
Read the manual , Use the mate paper, dont use all black target printed on LASER printer (but gray color seems to be OK). Or use better camera or try another angle of camera view.
What kind of camera is suitable?
The camera must support the recording of the video in VGA quality (640x480, 30 fps) or you can try some of the tested webcams.
How much cost a LaBr-gun?
It's depend on cost of 3D printing or used replica of gun. The parts for basic electronics cost about 5$.
Where can I buy LaBr-gun?
You can not buy it for now. But you can download it and build it, the source files are on thingiverse.com.
Is there some alternatives to LaBr-gun?
Yes, see the alternative "guns" page
See the support page.
It is safe to use by children?
Yes, but remember, you using the LASER device so be careful on your eyes.