There are many dog tag versions of knives, signaling devices and so on. This is Hardcase's take on a "Plan B" option concealing it as a dog tag.You can get single or double sided and the sides have been impregnated with diamond dust that allows you to cut through various metals.
You can place this tag together with the black rubber silencers and conceal this among your personal dog tags. In a pinch it could be used as a signaling device also.
I used this to cut the chain pictured below. It took less than 5 minutes which is pretty impressive. I did use poor technique and barely bent the edge of the tag.
Its a great escape and evasion device if your serving abroad.