First, see if the LED on your trainer remains constantly lit.
If it doesn't have an LED, make sure that once it is plugged in to the mains, you can hear the group of magnets moving slightly.
Then, check if your device has built-in ANT+ antenna. Some tablets and a few smartphone models have one, but in most cases, you will have to use the ANT+ antenna that we provide with the trainer or Bike and connect it to a USB port on your device.
Finally, remember that if your trainer is connected via Bluetooth to some device (PC, tablet, etc.), it will not be visible to other devices.