The Distance Cubelet detects how far it is from an object. It uses infrared light and is accurate between 10 and 80 cm. The sensor is directional, so outputs the distance to the object in front of the sensor. At 10cm, the block will output values near 1, and toward 80cm it will output values near 0.
Cubelets are magnetic blocks that can be snapped together to make an endless variety of robots. You can build robots that drive around on a tabletop, respond to light, sound, and temperature, and have surprisingly lifelike behavior. But instead of programming that behavior, you snap the cubelets together and watch the behavior emerge like with a flock of birds or a swarm of bees.
Note: Cubelets require a special battery and charger. You will need to purchase the charger separately.