"JoyGeek Heart Rate Monitor/Watch"
I bought this band for my wife, it was really easy to set up, literally seconds as it only needs the download of a free app to allow you to set up targets and personal profiles(We have iphones but it should also work on Androidstuff) screen grabs added. Its a USB unit which means that you simply plug in the watch to the laptop etc for it to charge up.
It doesnt have a button however its screens are changed with a light press of the bottom of the display.
You can also specifically record your activities by using a long press to start the timer. There are various modes such as Walk Run and Bike, I've added the photos to show you how simple the displays are then when you get back you can view the info on the App!