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

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!