Keep your Mountain Bike Tracked with Silenced AirTags 

I think the bottle cap cover is a good choice. It's the sort of thing a kid would but on a bike. It dousn't scream here is the air tag

AirTags will still send an alert to the thief's iphone notifying them that they're being tracked regardless if it's "silenced" or not. Sorry but AirTags are useless for this purpose.