まい：If you need a microphone,
but you only have a speaker you don't have a problem.
Both have magnets and coils that conduct sound
in roughly the same way.
So you can just plug a pair of headphones
into a stereo's auxiliary jack and crank the volume.
It's not quite good enough for karaoke
but you'll be able to hear even faint noises
like the disks in a safe's locking mechanism
clicking into position.
