Blimps Seem Like the Friendliest Kind of Indoor Flying Robots, IEEE Spectrum, 2017. 

Using a blimp rather than something with spinning rotors solves lots of common problems with UAVs, though it also creates a few new ones. A blimp is inherently very safe, since impacts, even with people, are more comical than dangerous. Without wasting energy keeping itself aloft, battery life is measured in hours rather than minutes, and hovering in particular is very energy efficient, since it’s the default state of the blimp. The tradeoffs are that dynamic movement isn’t really possible, outdoor operation is a bad idea, and even if you’ve decided to call your blimp “miniature,” it’s not ever going to be particularly inconspicuous. (see more)