HiRui Universal Sports Armband for iPhone 15/14/13/12 & Samsung Galaxy - Adjustable Running Phone Holder for Workout, Jogging, Gym - Sweatproof & Secure Fit (Large, Black) - Perfect for Fitness Enthusiasts & Outdoor Activities

I use these arm bands less to hold my iPhone and more to hold the Bluetooth Reader "Miao Miao" on top of my flash glucose sensor, FreeStyle Libre, but these HiRui arm bands work well in both cases.The *key* to these arm bands and what makes them superior to other similar arm bands is the section of silicone no-slip dots inside the sleeve. They keep the arm band on my arm and above the elbow.My arms are 12.5" and 13" in width: To snugly hold either phone or diabetic devices, I use the size Medium. This size ensures that the arm band will not slip down. I put the band on first, then add my iPhone 10 that is inside an Otter Box (phone in first works too).However, after a long day of wear, the Medium can be a little constricting to my arm and I have a pattern of dots on my arm after removal. This would only be an issue if you wear it for diabetic devices or other reason that have you wearing it for > 8 hours. To more loosely hold my diabetic devices, I use the size Large. The Large sleeve stays put with its silicone beads. I use this size arm band for around the house and when I sleep. It will still hold my iPhone on my arm.NOTE 1: I use either an elastic band by Miao Miao or a 3D printed holder to keep the Miao Miao Bluetooth device in place on top of the sensor underneath the arm band. Without these, it is possible for the Miao Miao to fall out, especially with the looser fitting Large size.NOTE 2: I use these arm bands for walking and low impact activities. I have not used these arm bands during activities that may jostle contents, such as running or significant arm movement. However, the pocket with top cover does completely envelope my iPhone 10, so I suspect the only issue, if any, may be slippage, not the phone coming out.For care, I wash these gently with detergent made for delicates and hang dry.I have all 4 colors of these bands and own 4 Medium and 2 Large bands so that I always have a clean band. The colors are much brighter than shown in the pictures. The pink is bright neon pink, the yellow is bright neon yellow and the blue is a deeper sky blue.The arm bands are well made and have two skinny pockets that go almost the length of the band and one large pocket for a phone. The latter also has a small hole with a well protected edge to enable corded earbuds to thread through. I'm not sure of the intention of the skinny pockets, but I use them for my chapstick.Lastly, I appreciate the reflective pattern on the phone pocket, which has held up to multiple washing and months of use, whereas other brands lost their reflective writings within a few uses.Overall, I highly recommend these arm bands for securing both phone and diabetic devices. I have 3 other types and brands of arm bands, and these work the best for me.