Not sure if these are just for disposable pens, but it seems a great idea.
Just checked and it’s only for disposables, doesn’t work with cartridge refill pens. Sorry
These are similar and work with some non reusable pens
http://www.insulcheck.com/supported-pens
I’ve been looking into one for my girlfriend, she’s 30 and still forgets if she has had her insulin or not, 26 years of being a type 1.