I was trying to make a simple detector to find whether a wireless charger is defective or not. This detector is a voice coil from an old hard drive connected to a LED. This appears to detect power from an electric tooth brush charger and an Ecolite charger. A 30 turn coil made from magnet wire connected to LED also will work. The voice coil appears to have the right inductance to resonate to 30 Kc, the usual frequency of wireless chargers. I am not repeating the procedure to take the voice coil out because that can be found on the web in many postings. Please see the videos. The photo shows the location of the voice coil in the read/write head of the hard drive.
The 1st video is an electric tooth brush charger and the 2nd is an Ecolite charger.