IIRC, most smartphone cameras can clearly detect IR, so another option is to wait til dusk, or darken the room, then scan it through your smartphone camera looking for pinpoints of light that show the IR bulb.
Ofc, doesn't work with cameras that don't have IR.
Most smartphones have an IR filter on the back camera, but don't on the front camera.
A good way to test that is by using an old-fashioned TV remote with an IR emitter and look for it to glow when pressing a button. It's a good way to test the batteries too!
Ofc, doesn't work with cameras that don't have IR.