Gen 1 contains both 3m tape and screws to make a permanent secure fix.
This gen 2 Is tape only and the tape isn't 3m it's cheap alternative which falls off very easily. There is no option to screw it down in this version.
While they are smaller than gen 1 they are much wider that gen 1 which makes them look messy attached to a standard upvc window frame. Gen 1 is narrow and fits on a frame easily making it look much nicer.
TIP Glue them down with a bit of general purpose silicone. It is easy cut free when needing to change battery etc. Dont do this if you and your neighbours enjoy being woken up in the middle of the night when the sensor falls off.
So avoid this and buy gen 1. This should never have been released.
Note to ring: Remember a sensor needs to be fixed down securely to avoid setting the alarm off. Don't release products which can easily fall off!