Currently there are 2 main types of hardware signing devices that work with Android phones (or mobile devices in general):
  • NFC-based: Tapsigner and Coldcard mk4 (and soon the Q1)
  • QR-based: SeedSigner, Blockstream Jade, Foundation Passport, Specter DIY, Krux and Keystone
So we have quite a number of options already and a far cry from just a few years ago when there were none. Check out this thread for examples/guides of how these signing devices work in Nunchuk: https://twitter.com/nunchuk_io/status/1659114136779776001