Hey everyone I am working on a project that is a lot harder than what I thought. It is a project for school. How can I detect a gunshot indoors without using an array of microphones? I had something going well with using microphones, but I would be breaking patents which I cannot do for this project.
One point to note : patents stop you selling what you build (if it infringes on them). But they don't stop you building one to test.
That's deliberate, because they are as much about communicating the patented technique as they are about protecting the inventor - to encourage the spread and growth of good ideas for public benefit.
In practice, the "communication" aspect is encrypted in legal jargon and is usually written to satisfy the letter of the "communication" aspect without actually communicating anything. If an inventor can get the protection of a patent without breaking the trade secret behind it, he has a good patent attorney drafting the claims...
Nevertheless. you have the right to build any patented invention to test that the published idea works, as well as to improve on it if possible. You just can't sell (or hire or lease or give away or benefit from) the product without some agreement with the inventor, unless you are prepared to challenge the validity of the patent in court (not recommended!)
So legally I think you can use a patented technique for a school project (though I Am Not A Lawyer) - with proper attribution of course - as long as you are gaining no material benefit from it.
The school may consider winning a competition or passing a course is a "material benefit", or they may impose their own rules for the sake of the competition - it may be worth asking your tutor or adviser.
A microphone is the easiest way to detect shots (well, plus some processing and communication).
You will need to collect actual data on how different guns sound indoors. When you do, please wear good hearing protection. I usually recommend wearing ear plugs under muffs when shooting indoors. Movies simply do no convey just how loud firearms really are.
With that said, you explicitly stated you can't use microphones (although you probably can, but I do understand how school projects can be).
You might want to look into creating a "burning gun powder detector". Kind of like a smoke detector, except much more sensitive and only alerts on certain chemical compounds. I'm not sure what all is out there as far as "smoke classification sensors" (maybe a spectrometer?), and you'll probably have to borrow a chemist or two to get a good profile on burning gunpowder.
Other than a big bang and smoke, firearms really don't produce anything else.
I am aware this sounds verry silly, but if you are not allowed to use microphones you could try to build something as simple as a breadboard with a couple of wires attached to some LDRs (Light depending resistors) hook those op to a serial monitor (you could use Arduino for this if you are familliar) and you can monitor diffrences in light... Ofcourse a microphone would be way more accurate. But the flash of a gunshot should trip a ldr. Again, this could be complete nonsense.