If you don't believe me then pretend I'm trying to write a Tom Clancy novel. If I was worried that I'd had a device embedded in me like the following: https://www.wired.com/2002/06/excuse-me-is-your-tooth-ringing/
how could I have my body scanned to have it removed? I remember being told it was very small and that it was too deep to show up in an MRI. I was told it was a speaker/microphone but it could have been a microchip.