I had this twice, a few years ago, and it proved my "white coat" syndrome. It doesnt really restrict you although you obviously have to do "normal" activities that day, dont go running a marathon because it will skew the readings. You attach it under your clothes and the cuff inflates every hour (not as tight as the doctor does it though, so it doesnt feel as bad, and you get used to it as the time goes on)
With me, I used to always have high bp when I had it done at the doctors because of "white coat" effect, then I had to go every month and have the nurse measure it and I got worked up about what the reading would be so that went up as well. I had two 24hr blood pressure readings in 6 months of each other and when the results went back to my doctors, they were in the "normal" category. I never got called back!