Mine sits in my jersey pocket now, used to be under my seat, but I figure it gets less vibration on my back than in the juddery seat bag... plus, if I need it in a rush I can get it without stopping the bike (if being 'chased' ) or without having to crawl to bike (if just crashed)

Before I had a seat bag I wore it inside my crop top in a plastic bag to stop sweat messing with it...