Bats have been using sonar to navigate and communicate for ages, and now humans can do the same, thanks to lightweight and efficient ultrasound microphones and loudspeakers developed by physicists. The devices owe their flat frequency response to graphene, which makes a stiff and responsive diaphragm far superior to those in today’s ultrasound receivers and transmitters. Biologists can even slap one on a bat to record its nightly ultrasonic conversations.