1. A method comprising: detecting an infrared signal with a piezoelectric device; obtaining an infrared signal representation based on the detected infrared signal; detecting a combined ultrasonic and infrared signal with the piezoelectric device; obtaining a combined representation based on the detected combined ultrasonic and infrared signal; generating an output representation based on the infrared signal representation and the combined representation; and transmitting an ultrasonic signal with the piezoelectric device in response to the detected infrared signal.