When I did cardio on the Elliptical and ARC Trainer at Planet Fitness my heart rate was not appearing on the display. Maybe it's because I have low blood pressure. I'm not sure. I didn't want to risk working out without seeing my heart rate. Even though the heart rate monitor on the Treadmill worked, I chose not to use this machine because it hurt my hips and knees. This meant that I was confined to working out on the Stationary Bike because the heart rate monitor operated fine. However, working out on the bike each gym visit became monotonous. Then, I found the Polar H10 Heart Rate Sensor. After I do my 2 hours of weight training, I hit the locker room. I run the Polar H10 band under the faucet to get it wet, and snap on the Polar sensor. I put it on right under the bottom of my sports bra. It's easily paired with the Bluetooth on your smartphone. I also listen to music on my phone, so it's with me when I work out. My heart rate is now transmitted when I work out on both the Elliptical and ARC Trainer at Planet Fitness. I can see my heart rate number on the displays for my entire workout! Best of all, my hands don't have to constantly hold the silver heart rate monitor handles on the machines. This product saved my life!!! I highly recommend it!!!I had previously ordered the M-XXL (26"-36").size, based on the sizing chart. It was larger than I expected. It fit fine on the smallest setting, but it would disconnect as I moved, and it would completely stop working in the water. Someone else recommended I try the smaller size, so I returned the M-XXL and ordered the XS-S (20"-26"). It fit snugly on the largest setting, but it didn't work AT ALL. Polar Beat wasn't recognizing the H10 when I tried to pair it. The bluetooth on my phone wasn't showing it eaither. I called tech support, they tried to help, but the trouble shooting steps didn't help. So, tech support did a three way call with Polar. They had me do additional trouble shooting steps. Consensus: I recieved a defective device, or a dead battery. The dead battery is less likely because the monitor only uses the battery when it is connected to the strap. So, unless the seller re-package a used device as new, I recieved a defective device. I am not thrilled. Polar use to be known for their quality, that's why my doctor recommended I use the H10, but this is the third Polar device I've had to return because it didn't work, or didn't work as advertised (also had to return a defective M600). So, my choices are:1. Pay to ship the device to Polar to be repaired under warranty, and wait an undisclosed amount of time for it to be repaired.2. Return to Amazon for a refund, and order a new one (unfortunately this is the most accurate heart monitor that can be worn in the water)I picked the second option. I'm thankful that this was a Prime item.I have used a Polar H1 sensor with a T7 watch for the last couple of years. When decided to switch to bluetooth, I did some research and originally purchased a Wahoo Tickr X instead of staying with Polar. It was a mistake and I returned it a week later. There were so many issues with it but one of my biggest things was the bluetooth connectivity was horrible. I ordered the H10 the same day and haven't been disappointed. The metrics are very accurate.I love the update they have made to the strap.I thought the old strap was comfortable, but this new one is even better. I have an Android so the apps aren't the best, but I can purchaser different options on the app. The basic app gives me what I need right now. So far, I'm extremely happy.I really love this heart rate monitor. It's quite comfortable, and it pairs easily with the Polar A300 watch that I have. Combined with the watch and the related app, it tracks your heart rate through your recorded workouts and charts out your heart rate over the workout. It's really cool to see! You can tell when you're making an effort, and when you're phoning it in. I actually hate it when I forget this thing at home, because I feel like my workout is much less effective.I've had for approximately 1 month, I use it for about an hour 5x a week and it's still on the original battery/ no issues.Does not work for swimming, otherwise it works fine.I contacted Polar about this and here’s what they say:“Thank you for contacting Polar.Pool water with a high chlorine content and seawater may be very conductive and the electrodes of a transmitter may get short circuited and ECG signals cannot be detected by the transmitter unit.Jumping into the water or strenuous muscle movement during competitive swimming may cause water resistance that shifts the transmitter on the body to a location where it is not possible to pick up the ECG signal.The ECG signal strength varies depending on the individual's tissue composition. The percentage of people who have problems in heart rate measuring is considerably higher in a water environment than in other use“llevo con este producto mas de 3 años y se ha comportado de forma excelente! gran precision para medir la frecuencia cardiaca y facil conexion con multiples dispositivos incluso otros de otras marcas. como Wahoo, Apple y Garmin.Worked great for the first 2 years... Now going on the 3rd year and it glitches all the time.It will stop connecting to the watch. I've replaced batteries and I always make sure I clean it after each workout. I use the electro jelly.So it is very accurate because it's close to your heart.... But to be honest, it just grosses me out each time because it's soaking after each use...The whole process kinda sucks, put the jelly on, strap it, connect it to the watch.... Retry to connect it to the watch... Wash it.I have owned this for 5 months now and am glad I chose this over other brands.The monitor attachment is very sturdy/ chest strap fits snugly/ strap clip is super easy to use. I have never had issues with slipping.The sizing is listed as XS-S (20-26 inches) and M-XXL (26-36 inches). If you were as confused as I was by this, it is the length of the strap unadjusted and unstretched.For me the length of 20 inches was just over half of my actual chest size (32inches).I am a UK size 8 and the XS-S size fit me perfectly straight out of the box without any adjustment.It’s difficult to know how accurate the HRM is as I don’t have anything to calibrate it against. Even so saying this, I do get similar results from a setting e.g. aerobics or cycling.It doesn’t seem to be thrown off by lots of jumping exercises, and equally is not confused by low impact e.g. cycling. Which was my main concern (inaccurate monitoring – which I found to be the case when wearing a wrist device).The app is OK. It provides lots of different types of exercise categories to record and voice instructions tell you when you have hit certain BPM etc. It tracks GPS accurately and shows you a little map of your route and where your heart rate sections change.The Bluetooth links well to the HRM – which means you can record your HR without taking your phone with you. And simply download them later to the app. However it does mean you can’t track GPS if you use this option because it’s just a sensor, not a standalone GPS tracker.The biggest negative for me is the app, not the HRM. It has very limited functionality and there doesn’t seem to be any way to export the data that is recorded, or to clear all the data without individually deleting every record (for which I have 100’s now!) I would like to be able to record a weeks’ worth of exercise, and then clear it to start over.However even so - the HRM will connect to a multitude of other apps – strava/apple heart rate monitor so you are not restricted by this. Just needs a bit of investigation to find a better solution.Over all very good value for money.I have a Fitbit Charge, which has been great! But I found that it was not picking up my heart rate when I would do any high intensity activities. I wanted more motivation especially for the HIIT related activities. This Polar H10 chest strap picks up the HR really well during anything HIIT related . You can track your activities on your phone. It gives you a history of your personal best which helps you motivate yourself more. If you're running you can watch your HR as you're running. I think it helps you get motivated and pushes you.I haven't used it for swimming but plan to try it.I ordered the x-small/small which fits nicely but it is on the biggest it will go. Currently I measure 35" chest relaxed. Its pretty darn accurate measured against my doctors equipment and picks up quickly on alterations in my heart rate so I can adjust and control it rate better. It even detected my freak spiking events where it jumps from a steady 140 to 180 for a second or two then back down again. I am so impressed with this device. Also polar beat app is great and has a wide range of activities in its data base though not sure how each one differs. It Took a bit of time to set up the second time use because my phone saved the Bluetooth pair so wouldn't connect to polar beat. I had to forget the positing and restart my phone but only had to do that once. Now I just connect and go. I have wasted so much money on fit bit devices that fail to give an accurate reading of hr, I wish I'd started off with this.It will be great for when I train in the gym and have my phone near me to see the Polar Beat App screen.When I go for a run it monitors my heart rate well, giving run time, calories and a summary of improvements made as a result of the exercise. These are seen after the run on the Polar Beat App, unless you take your phone with you.The information downloads quickly and the App is easy to use with a good range of exercises to choose from.This item would benefit from a compatible watch to obtain real time data such as Pace, HR, and GPS tracking of the route.