Yesterday, I took my HTC one x to work with me along with my note 2, I stuck the X in airplane mode (there is no sim card in it) and placed it in my left pants pocket. I had the note 2 as my primary device. The extra device was in case the note messed up bad, or perhaps to sell.
Anyway, after a couple hours, while working, I kept feeling this weird warm sensation in my pocket every time I leaned up against something. It dawned on me to stick my hand in my left pocket and when I did, the phone was roasting! The one x camera had activated. It had been on so long that the battery went from 100% down to 18%
Good thing I was not using the device by itself. I left the charging cable at home. I cannot use a spare battery. So, it was a good thing I did have another device on hand. Spare charging cable going with me when possible now