I saw an article on reddit today about a pill that motorola has developed that has been FDA approved already.
"A quick soak in your gastric juices turns the pioneering pill on, triggering it to transmit an 18-bit, EKG-like signal from your insides. The ingestible micro computers (thankfully silent) signal would then automagically unlock your smartphone and other gadgets. Yes, youll actively be your very own password beacon for as long as the pill is still inside of you."
This seems like it could be useful for hardware wallets for large face to face transfers or a cold storage wallet.