Single-button app on your phone: https://ifttt.com/do_button

I like particle photons. That can used in these: https://www.particle.io/products/hardware/internet-button

No hacking required.

I bought a Flic button which works pretty well, using it at the office for hour tracking; it's more pricy though. Normally they are tied to a phone, so if you want it to work for multiple users, you need their hub as well.

You could build your own like this http://www.simpleiothings.com/build-a-10-wifi-smart-button/