OpenTag is an Arduino-compatible open-source inertial measurement unit (IMU) for recording high speed motion sensor and depth data to a removable microSD memory card.  OpenTag uses a rechargeable lithium polymer battery so you can reuse it unlike other data storage tags. Data are stored to CSV text files for easy analysis.

Applications include waterproof compass datalogger, high resolution water-level logger, and animal tag.



  • 3D Accelerometer

  • 3D Magnetometer

  • 3D Gyroscope

  • Pressure (depth)

  • Temperature

  • RGB light sensor

  • Speed sensor (experimental; available upon request)


  • Dive behavior

  • Pitch, roll, yaw

  • Bioenergetics: ODBA and VDBA

  • Fluke rate

  • Feeding behavior

  • Waterproof compass datalogger

  • Water level logger


A single rechargeable lithium battery will run OpenTag continuously for 7 days with all sensors.  The double battery version will run for 14 days.

The IMU motion sensors run at 100 Hz simultaneously. 

The pressure, temperature, and light sensors are sampled at 1 Hz.

OpenTag integrates a small aluminum housing with an o-ring to allow access to the memory card, recharge the battery, and the power switch.


OT3-BRD: OpenTag3 Board unpotted, battery, 32 GB microSD card

OT3-KIT: OpenTag3 Board, Ring and Lid Set, battery, 32 GB microSD card for potting your own

OT3: OpenTag 3 Potted with 32 GB microSD card

  • Depth rating: 300 m

  • Dimensions: 10.5 x 4.7 x 2.2 cm

  • Weight: 110 g in air

  • Power: 1 Rechargeable lithium polymer battery

OT3-F-V-S: OpenTag3 potted with float, VHF, suction cups, burn wire, 32 GB microSD card

OT3-F-V-P: OpenTag3 potted with float, impeller, VHF, mounting plate, burn wire, 32 GB microSD card


3D Gyroscope: Measures rotational velocity. Use with accelerometer and magnetometer for accurate measurement of 3D motion.
3D Accelerometer: Digital accelerometer for motion and tilt sensing
3D Magnetometer: Measures magnetic field strength for compass orientation

Pressure: 0.5 cm depth resolution to 300 m
Temperature: -40 to 85 C +/- 0.5C. Resolution 0.015 C

RGB light sensor




Original Open Tag


OpenTag Setup (Windows) Script file generator

otAHRS OpenTag MATLAB software to calculate pitch, roll, and yaw