Hello guys,

I am building an RF tag that will transmit some data using a microcontroller and a 433 Mhz transmitter. But I do not want to place any buttons on the device nor have it be on at all times. So I was wondering is there a way to create a magnetic field at the source to generate an induced current in this tag to perhaps flip a switch to turn on the internal battery? And once the tag is out of the fields range the switch will open again?

I know systems such as the Sunpass or other electronic toll payments use something like this.

If anyone has any information on how this can be done, please help.

Thanks.