Interesting; I haven't considered an audible alert. I'm assuming you mean an audible alert in the bike's sound system.

When the receiver detects an alert status from the sensor, all it can do is turn on a signal. With an LED the process is simple; all that needs to be done is to use this signal as the power source for the LED. Receiver detects an alert... turns on a signal... the LED gets power and lights up.

However, even my digital multimeter generates little beeps when I press buttons on it. There has to be simple tone generators out there that can be used here. Receiver detects an alert... turns on a signal to power the tone generator... sound is created. Hmmm... yes I think that's a possibility! The output of the tone generator would just need to tie into the sound system.

Now that I'm past the hard part, these will be easy to make, and the more I make the cheaper I can offer them. I currently have these built on generic prototype PCB's from Amazon but for ruggedization for automotive use these will need proper PCB's made which are cheaper in higher volumes.