Methods, systems, and apparatus, including computer programs encoded on computer storage media, for reduction of false detections using an ultrasound emitter. One of the methods includes obtaining sensor data captured by a sensor of a property monitoring system; detecting an object represented by the sensor data; determining that the object represented by the sensor data is likely a non-object of interest and being detected as an object of interest; and in response to determining that the object represented by the sensor data is likely the non-object of interest and being detected as the object of interest, sending, to an ultrasound emitter, a command to cause the ultrasound emitter to emit ultrasonic sound around the sensor.