Query if the characteristic has been subscribed to by another Bluetooth® Low Energy device.
bleCharacteristic.subscribed()
None
// Bluetooth® Low Energy Battery Level Characteristic
BLEUnsignedCharCharacteristic batteryLevelChar("2A19", // standard 16-bit characteristic UUID
BLERead | BLENotify); // remote clients will be able to get notifications if this characteristic changes
if (batteryLevelChar.subscribed()) {
// set a new value , that well be pushed to subscribed Bluetooth® Low Energy devices
batteryLevelChar.writeValue(0xab);
}