You have not downloaded and installed the app. Follow the instructions in “GENERAL SET-UP & APP."
You have not installed the battery or batteries. Follow the instructions in "HOW DO I INSTALL/REPLACE THE BATTERY?"
Your activity tracker's battery/batteries are low. Follow the instructions in "HOW WILL I KNOW WHEN THE BATTERY IS LOW OR NEEDS TO BE REPLACED?"
Your activity tracker may not be close enough to your phone. Move your activity tracker closer to your phone.
Bluetooth may be disabled on the phone. The app will notify you that Bluetooth is not on and will ask to turn it on. Try enabling Bluetooth on your phone using the phone’s Bluetooth settings. If it is already enabled, try turning Bluetooth off and on.
Your activity tracker may need to be unpaired and then, reconnected to the phone. Follow the instructions on “HOW DO I RE-PAIR THE SAME ACTIVITY TRACKER WITH THE APP?”
The device might be "sleeping" from lack of activity. Double tap the device to "wake it up." This will allow the phone to connect again.