So in 2007, we figured out how to put a personal computer literally in our pocket with a fancy touch screen and stuff. Then we figured, why not put them on our wrists? Hell, why not dump a tiny computer on the end of a badminton racket? We have seen tons of technological innovation in the past 10 years, and it's unsurprising we're looking at what we can do with it in sports. The idea of having a little sensor on the end of your racket accomplish the same task as a high speed camera, at the low cost of £30 or so, seems really appealing. But are they as useful as they say they are? Watches: Fitbit, Pebble, Garmin and now other watches like the Apple Watch are incorporating features for monitoring your calories, your heart rate, your sleep, everything you could imagine. I'm sure you've seen one at some point, and they usually retail for £100-£300 depending on which model you choose. I think one of the most popular uses for these devices is calories burned. However, to calculate how many calories you've been burning, the watch looks to your heart rate. Most of these watches will use a laser or optical sensor on your wrist, the sensor then detects changes to look for when your heart has had a beat. This is extremely unreliable, with wild fluctuations depending on brands. Especially at lower heart rates, the discrepancy can be enormous. What you further have to account for, is that in most of these studies they're looking at runners, or indoor cyclists (on an exercise bike or turbo trainer). Unlike racket sports, you aren't routinely tensing your wrists; while you may have to do this on mountain bikes, you certainly don't need to do this in a laboratory. In a racket sport, you're using your wrist at least once every 2.5 seconds as a core part of the game; even if you're just clearing, this is evidently an issue. At one point whilst using a FitbitHR and doing intense multi feed drills, my sensor reported I had climbed over 140 flights of stairs. That should tell you how accurate the metrics used by these devices are: they actually aren't very reliable at all. They look for very specific things, and if they miss or otherwise misidentify these things you end up with spurious data that doesn't tell you a lot of useful information. Racket Sensors: We all want to know how fast we smash, it's a pet curiosity: we see LCW smash and a satisfying 404kmph pop up in the corner, and we want to know how we stack up against that. These sensors promise us this information, but again, they work on accelerometers looking for very specific things. If my wrist watch can flagrantly lie about me climbing 140 flights of stairs, why would this device be more accurate? These devices even strive to tell us how many of each shot we've played, but did you consider it misread you scooping the shuttle up for your opponent after a rally as a net shot? Or when you swished your racket for fun, that it read that as a smash? These devices can not provide you with a comprehensive pool of information on your play; they're based on a very small amount of technology, with a very limited scope. One of the greater issues is that it doesn't even tell you how it's calculated: is it measuring your smash speed, your racket swing speed, where is point A and where is point B? They fundamentally lack key information points. They're also utterly awful to have on the end of your racket; not to mince words, they are absolutely noticeable. No matter how light they claim they are, or how you won't notice them, you will. You absolutely will. Go and get a big blob of blu-tac and stick it to the end of your racket, tell me how quickly it irritates you. 2 rallies and you'll hate the thing being there. It's deeply inconvenient, distracting, and takes away from the feel of your racket - it will defamiliarize you with the feel and touch of your racket. So what are these devices good for..? These devices are a self-comparative metric. If your racket sensor tells you, 2 months ago your swing was at 170kmph, and now it's 250kmph, then you can likely conclude there has been some change in your swing, and that there is probability it is a good change. If you see you now exercise for 45 minutes longer on average than you did 2 months ago because your watch told you, congratulations, your heart rate is higher for a little longer. These devices are good at making a sign post for you, to then establish a trend in information. They are not however, practical for telling you real world data such as swing speed or heart rate in a reliable fashion. If you want to look at general trends in what you're doing, these types of devices are ideal. If you want real metrics, you need better equipment. If you want better quality data, get yourself a camera or a coach. They'll serve you better.