This is a cheap, easy to use hrm. I was a little disappointed that only one function is visible at a time but it's used as a stopwatch primarily and a back up hrm second.
The chest strap fits me well, actually more comfortable than my old polar hrm.
It did not work properly when I bought it so I changed the batteries. It still did not work properly - the HB display erratic and ultimately unpredictable. Sometimes no response. Tried wetting my skin where the contact is made. Also tried running without a T-shirt but the signal still intermittent. Not worth the hassle of changing so it's in the bin!
I'm sorry you have had a problem with the synchronisation of your OnRhythm50 Chest strap and Heart Rate Monitor. I will ask the product manager if there is anything else that can be done other than wetting the sensor. It's a while since I've used mine but although it did not connect dry, I had been OK when I applied some water the sensor.
If you change your mind regarding the return you have up to 2 years under the product guarantee should you be in a Decathlon store.
If the purchase was made online and you wish to return by post our customer service team will be happy to help.
David Daker Commercial Director DECATHLON