If you're like me, you've dreamed of being a dolphin - smoothly gliding through the water. Using your echo-location abilities to detect tasty fish treats. Until genetic modifications catches up with our desires, we'll just have to make do with these handy HC-SR04 Ultrasonic Sonar Distance Sensors and a pair of flippers. These ubiquitous sensors are really common in robotics projects, but they can also be used for automation, interactive art and motion sensing. They work at about 2cm to 400cm away, but we think 10cm-250cm will get you the best results.
These sensors are fast, fairly easy to use, and low cost. They do require powering from 5V for best results: connect GND (ground) and VCC to 5V power. While the Trig signal can be 3V or 5V, the 'return' Echo signal is 5V logic. For that reason, we include two 10K resistors, use these as a divider to convert the 5V logic level to a safe 2.5V that you can ready with your 3V device.
You can use this sensor with Arduino, CircuitPython (for microcontrollers or Raspberry Pi) or MakeCode
We carry a large variety of distance sensors here if this fellow isn't what you're looking for.