HRM Newbie questions

Leiterch

So I have just started getting back on track about my weight loss and overall fitness shape. I had this site recommended and so far I am very glad I stopped in to check it out. I have been reading a lot of posts on here and have taken away a bunch of useful information. I do however have a question when it comes to HRM's. Do you have to wear the chest strap for all monitors to work? I have been looking into the Polar T7 or one of the Timex IronMan versions. I am looking for something that would work from a day to day standpoint, but I can't get clear definition if you need the strap for them to work properly.

Any advice would be great. Thanks.