Fitbit

I have been wearing one for 2 years now. They definitely help you to be more active. I have one that also monitors your heart rate, as the heartrate thingy sticks out below the band I would not ever wear it on my lymph node removed arm. Even though I wear it loose, there is often an indentation, particularly in hot weather. Works just as well on the other arm (you can change the settings if it is your dominant arm or not).