You just gave me a cool idea. You could do this by fitting small tuning forks (or similar) to a mechanical keyboard. Bonus points if all of the forks are tuned to a pleasant scale.
Then all you need is a microphone running on the destination device. Obviously this is insecure but could be fun anyway.
Then all you need is a microphone running on the destination device. Obviously this is insecure but could be fun anyway.