I received one of these a few years back after having done a first aid course. It's a CPR face shield held inside a small nylon pouch. The pouch itself, has split ring which allows you to attach keys and other items to it.
|Attached with keys and miscellaneous items|
In the unfortunate situation where someone is passed out or not breathing, this face shield allows you perform CPR without having to worry about breathing or swallowing that person's blood or saliva. This helps to reduce the risk of getting transmissible diseases such as hepatitis or HIV.
|Face shield contained within|
Considering what is contained inside, the package is fairly small and light, though a little on the bulky side. The shape of the package makes it hard to take measurements but it's roughly; 55mm (H) x 55mm (L) x 15-20mm (W). It weighs around 14 grams.
To be honest I don't carry this one around on my keychain, but I usually keep in my laptop bag which I carry around with me a lot. Thankfully I have never had you use it, but it's nice to know I've got it there if I need it.
I'm not too sure where you can get them from in your own country. I did bit of a google search for you guys and came up with a few australian websites which sell these or something similar. The first link closest resembles the CPR face shield that I have: