iPhone says it is in constant use. What could cause it?

[Hoyboy]

I took my iPhone out of my pocket at the end of work and discovered most of my battery had gone. I don't use at all while at work so it usually has around 80% by the end of the day. To my surprise more than double of that had been used. Any ideas what might have caused it?

 

[Sone3D]

Wirelessly posted

It once happened to me and turn out to be Safari iCloud bookmarks sync.

 

[Hoyboy]

I don't think it's that. I don't have it turned on