If your speed sensor SPD61 / C61 can't work well, pls try the following to fix the problem:

Firstly, pls ensure your sensor is installed correctly.

See the articles below for proper installation instructions:

Installing Speed Sensor SPD61

Secondly, pls replace a new battery for the sensor.

If you're still having trouble, please contact support with the following information, we'll be happy to assist you further.

1. SN at the bottom for the cover.(example)
2. Replace a new battery and check if it flash lights or not,and show us a similar video to us for further analysis:

https://www.youtube.com/watch?v=VsJ329K2Ufw

The correct way to insert the back cover :

Usually, most cycling Sensor issues can be resolved by completing the following steps:

1. Replace the battery - data can fail to transmit properly on a low battery
2. Ensure pairing made only through app - If the sensor is already paired with two Bluetooth devices, you should pair using ANT‍+ technology or remove a Bluetooth device.
3. Check the battery connection - while the battery is removed, flex the metal prong that connects to the battery by pulling up gently. If the prong becomes pushed down too far, it can fail to make a strong connection with the battery.

4. Check for interference.

If none of these resolves your issue and the LEDs are still functioning, you may be experiencing signal interference which can be caused by the following:

Previously paired apps or devices:

The most common cause of interference is a previously paired app or device.

It's important to unpair your sensor from all other apps and devices (including previously paired computers, phones, watches, or APP, etc.), force stopping apps or shutting down additional devices before pairing with another.

1). Physical distance: Signal strength degrades as distance increases. For best results, keep your device less than 5 feet from your RPM sensor.

2). Wireless signals: Any devices that transmit wireless signals or electromagnetic fields can cause interference, especially these:

• Wireless routers
  Wireless or Bluetooth headphones or speakers
  Bike lights
  Video recording devices (GoPro's, etc)
  Wireless video receivers or transmitters (Chromecast, AirPlay, Roku, etc.)
  Fans (especially large ones): avoid placing between your device and TICKR
  Cordless home phones
  Satellite or cable boxes
  Microwave ovens
  Power sources (power lines, boxes, lines in walls)
  Wireless mice/keyboards
  Certain TVs (especially WiFi Smart TVs) or monitors
• Anything else that can transmit wireless signals, including radios and baby monitors

5. Physical barriers: Walls, metal desks, counters, and even the human body can degrade signal quality.

If any of these are affecting your signal, try uninstalling, disabling, or shutting down offending devices. Alternatively, try relocating the sensor further from the source of interference or to a new environment completely.