I went through half a dozen Sports Instruments heart rate monitors over about half a dozen years. The company went out of business several years ago. They had a chest strap and a wrist watch unit. The chest straps never quit, the wrist watch units I suspect were not as waterproof as they were supposed to be. I used them on my handlebars, thus they occasionally saw rain. An example of one dying in the photo. It had four buttons and when I changed the batteries in them they looked like the buttons were in fact not waterproof at all.



Since then, I have bought three Sigma iD.GO heart rate monitors. They are also a wrist watch type, they use a chest strap. So far, no problems with them but I have only had them for about 10 months. I have one each on three of my bikes, I use an old handlebar adapter mount from my older Sports Instruments HRMs. The Sigma HRM did not come with that handlebar adapter mount.

The photo below is of my cockpit on my bike this past June and July when I had a five week bike tour in the Canadian Maritimes. The Sigma lived on my bike and was exposed to every rain event, and there were several, some of which were multi-inch rain events. There is only one button and that button appears to be well waterproofed since it never quit even though it was rained on a lot. The Sigma is at the bottom of the photo, to the left of the inclinometer which is to the left of my bike computer, which is to the left of my GPS. You can see the word Sigma on it, the upper number on the Sigma display is 115, which was my beats per minute at the time of the photo. The readout has big enough digits that I do not need my reading glasses to read it.




Here is a link at Amazon to the Sigma
https://www.amazon.com/gp/product/B0728KH8GW/

I specifically wanted a cheap one that had no bells and whistles, just heart rate so I could tell if I was running too many beats per minute on uphills, etc. Sigma met that goal. And since it is only a wrist unit with a strap, I do not need a phone or anything else like that to make it work.

The Sigma iD.GO is compatible with my old Sports Instruments chest straps, so I am actually still using my Sports Instruments chest straps. These straps are the older type ones (1980s technology) that are not paired with a receiver, they predate the ANT+ or the other newer ones that you have to pair with a receiver. These older type chest straps also work with the exercise bikes and stairmasters at my health club for when I work out there on cardio machines in the winter.

So far I have not used up a battery on any of my three Sigmas, so I can't say how hard it is to replace the battery or which battery it takes.

If you are new to heart rate monitors, be warned that the chest straps work best if you have sweated a bit. On dry skin they do not have a good electrical contact and will not function well. When I use one at the health club I often will lick the electric contacts on the chest strap first to wet it before I put it on so that it has good contact with my skin. Without that and I might not get a good reading for 10 or 15 minutes.