This is a DIY Cell Phone Klick Quick Button by Roman UrsuHack. You can get these for about $1 on eBay or just over $2 on Amazon but building your own might be fun and chances you have everything you need laying around. Great idea to add some extra simple functionality to your phone, turns out the simple headphone jack is getting more versatile as time goes on. I still remember when it was just for headphones. 🙂 I am sure some people these days think of it as the Square Credit Card Reader jack.