Hrm Tri question

So I read that the hrm tri saves hr data and syns later on with a garmin device. My question is does an activity have to be active in order for the data to be synced? 

I ask this because I'd love to be able to monitor my hr at work however I cannot wear my watch on my ankle or wrist due to uniform restrictions. Would I have to have an 8 hour activity run I g in the watch in order to pull the data from the hrm or will it sync regardless?