Not really. The human ear can perceive down to 20Hz, and below that, you can't perceive it actively, but the subconscious starts playing weird tricks [1]. Plus,

Not really. The human ear can perceive down to 20Hz, and below that, you can't perceive it actively, but the subconscious starts playing weird tricks [1]. Plus, you'd be limited to X Hz/2 bits per second. Your better bet is getting something to drive an occasional chirp at 20k hz or so, which would be imperceptible to most people. [1] http://skeptophilia.blogspot.com/2011/02/ghost-in-machine.html http://skeptophilia.blogspot.com/2011/02/ghost-in-machine.ht...