She was cute, but she forgot to mention that most digital cameras now (including cameras in smart phones) have IR filters and won't show IR light.

The back facing camera on current iPhones won't show IR at all and the rear facing camera will display it very faintly.  I think the IR filter on the back facing camera started with the iPhone 4s.

This has been a good trick/tool for a long time, but as cameras get better, that little IR card might make a better indicator.