Both my husband and I use these with the Polar FT7 watch for a wrist display we can check during runs and Runkeeper for data tracking, and we love them.I have tachycardia (POTS) and it’s important for me to both exercise frequently and monitor my heart rate while doing so, to make sure it doesn’t get too high – even on meds and other treatment, it’s easy for me to exceed 80% max HR in the first minute or two of a run without pushing myself much. The Polar sensors have been great for this – they’re very reliable. It helps immensely to be able to tell when I’m tired because my POTS symptoms are worse versus when I’m simply tired.Also, *if* you use a Polar wrist display or the Polar Beat app (more on that below), Polar uses a very accurate algorithm to calculate calories burned based on heart rate (plus age, weight, height, and gender). This is great when I’m counting calories for weight loss.I also love that the sensor detaches when you’re not using it, so the battery doesn’t drain as fast.One of my few complaints is that my husband’s monitor seems to be more prone to losing signal or showing a clearly incorrect heart rate (very high or very low) than mine is (although mine does that occasionally). This may be a problem with the watch (apps don’t always pick up the same inconsistencies). I’ve also had it happen when the band wasn’t tight enough, or the battery was close to dying – and I suspect my husband’s chest hair has something to do with his more frequent inconsistencies. None of this is a big enough deal to drop a star, especially compared to previous monitors I’ve used.Watch Pairing: It pairs easily with the FT7 watch; we’d both been using those with the included non-bluetooth sensors, but the watches picked up the new sensors within 30 seconds. We didn’t need any special pairing procedures; the watches picked up the signal on their own – and as far as we can tell, they don’t get mixed up even when we’re running side by side.Phone Pairing (Android): The important thing to remember here is that you don’t pair the sensor with the *phone*, but with the *app*. If you go into the Bluetooth pairing settings in your phone, as you would to pair a headset, it won’t find a signal for the heart monitor. This is normal. Instead, make sure Bluetooth is on, go into the app you want to use, and check the Settings. Most third party apps have a setting you can turn on to use a heart rate sensor. If I remember correctly, MapMyFitness handled both that and sensor pairing in the Settings when I used it; RunKeeper handles pairing from the map screen (turning on the sensor setting adds a gray heart in the bottom right corner of the map, which bounces when it detects an unpaired sensor and turns red and beats when it’s reading your HR). Check the FAQ on the app’s website or do a search if you’re not sure.Apps (Android):- Polar Beat (Polar’s app) is okay for stationary or studio workouts, but just okay. It does give you a nice HR chart and that lovely accurate calorie count that Polar is so good at. However, you’ll want to keep it on your body if you’re moving around a lot, because this app loses signal very easily if you get your body in between the sensor and the phone. For outdoor workouts, there are much better free apps available; Polar Beat would frequently fail to map my run at all, or stop somewhere in the middle when it lost GPS signal, and its distance measurements weren’t particularly accurate. I haven’t used it for runs since March 2015, so this may have changed, but I’m not holding my breath.- Third Party: I haven’t found an app yet that doesn’t pair easily with this, since Polar is the standard in heart monitors. I’m a fan of Runkeeper since it gives you access to your heart rate charts without a subscription, but that’s personal preference. I’ve also easily paired it with MapMyFitness, Endomondo, some random app that’s supposed to calculate your “morning readiness” from heart rate, and probably some other workout apps I’m forgetting about. Take your pick – most of them have pairing instructions on their websites if you need them.- Multiple App Pairing: You can use the monitor with multiple apps simultaneously IF the apps allow – some don’t. For example, I was able to use it with MapMyFitness and Polar Beat (for accurate calorie count) at the same time without problems; Runkeeper, however, won’t even detect the monitor if another app that’s running is already using it. For best results, use the window cascade feature to look at what you have running in the background, and close everything that connects to the monitor if you don’t need it. However, there’s no problem with having multiple apps installed and paired with it as long as they’re not all running; you don’t have to re-pair each time you switch apps.For reference, both my husband and I have HTC One M8 phones.Multiple Devices on Signal: I’ve had no problems with the monitor transmitting to the phone and watch at the same time, nor with it sharing the phone’s bluetooth signal with headphones.Random tips: If you can’t get your phone to pick up the signal, do the usual (reboot, close and restart app, turn Bluetooth off/on). Then check to make sure the strap is snug, especially across the front of the chest, and make sure the sensor is snapped in securely. You can wet the sensor area of the inside of the strap (the vinyl-like part) with water (or, if that’s not enough, with salt water or electroconductive gel) if you’re still having problems. After that, check the battery. I also find that sometimes the watch, if you have one, is a more reliable test of whether it’s working than the phone is.Changing the Battery: Pretty straightforward DIY. I’ve found it’s easiest to use a narrow key ring to turn the battery cover, and make sure to *pay attention* to how the battery cover is oriented in the “loose” position before you remove it, because it’s really hard to loosen it again if you replace it in the wrong position and tighten it, and it’s not water/sweatproof unless it’s seated right. It fits tight, but I had no trouble with it even though I’m sometimes not strong enough to open sealed jars.In summation, this is awesome and I love it. Mine has been working fine for almost a year with one battery change, my husband’s for 7 months. We’ll see how long the fresh batteries last.