Small, inexpensive cameras are everywhere now. They have WiFi available, too.
Here we put a small wifi camera on a laser for a handgun. Any phone nearby can see the laser in the broadcast image.
Really fun to use, though I'm not a big fan of gadgets on my guns... especially electronic gadgets. Here we put the camera in the handle of a cheap foregrip.
I think these would be most fun for Airsoft. Easy to shoot around a corner, not life critical.
Here is a different mount on another cheap laser.
The camera weighs only ~1.5 ounces, so it is hard to notice on the end of a handgun. They are pretty inexpensive on eBay, too so that makes them even more fun.
Also, the camera can detect IR light - so if you have an IR flashlight or spotlight, you have night vision!