Using an AAA battery enclosed in a rubber housing at either end, with a length of ‘fibre optic’ rod in between, makes for a highly visible strip of red light.
The housings at each end have pen-style clips on them, so you can attach them to clothing, bags and so on. They also come with handy rubber straps that allow you to mount them in various different places on your bike (the back of the seatpost or seatstays, for example) – making them a versatile rear light that’s easy to fit and remove in seconds.
The run time in flashing mode was a little less than the claimed 70 hours; we found they lasted 65 hours, at which point they were so dull there was no point using them.
We had no problems with water ingress and they’re definitely shockproof. Having a pair of them, set off at different times to enable them to flash out of sync, gave a great deal of visibility from all angles.