Seeed Grove Motion Sensor, Control and Actuator Modules - Seeed Studio 101020010, The Grove Ultrasonic Range Finder from Seeed Studio emits ultrasonic pulses and times the return signal to establish the distance between the sensor and a reflective object.
It can measure distances between 30mm and 4m.
Seeed 101020010 Grove - Ultrasonic Ranger Distance Sensor 3cm to 4m 5V