Invisibility !
Just spent 10 mins playing hide-and-go-seek with a hot air balloon! Been to the ATM in the village - on my way home saw the balloon quite low in the sky - but - by the time I had dragged my trusty Canon out of my handbag - it had vanished. However I could still hear it so followed it's route - kept having tantalizing glimpses then - finally - it appeared again just above these trees. Canon - point - click - got it!
Here is a photo of a Hot Air Balloon wearing a Klingon cloaking device - and laughing at the twit with the camera!