For the Z9, if that's what you have it has a weird function to sometimes be paired to an old phone, or has some type of memory problem. You can either 1) Wait until the bluetooth fully dies and repair by holding the Ant button then waiting for it to stay steadily blue/purple or blink red/blue and search for it from your phone OR 2) Hold down the + & - volume buttons and the Ant button to reset it. It happened to me a couple of times and I just went to buy a new bluetooth after a few months. If you look at the manual it tells you how to reset it.
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For the Z9, if that's what you have it has a weird function to sometimes be paired to an old phone, or has some type of memory problem. You can either 1) Wait until the bluetooth fully dies and repair by holding the Ant button then waiting for it to stay steadily blue/purple or blink red/blue and search for it from your phone
OR
2) Hold down the + & - volume buttons and the Ant button to reset it. It happened to me a couple of times and I just went to buy a new bluetooth after a few months. If you look at the manual it tells you how to reset it.