A female bechstein's bat (Myotis bechsteinii) that was captured and tagged with a sender during my work as bat biologist.

She carried a sender on her back that looked like a tiny jetpack. X3 She led us to her nursery roost with many conspecifics and baby bats! So we can preserve the area where they rear their babies.
Senders fall down after a week or so and only weigh less than 1 gramm (about 0.29-0.39 g).