I purchased two of these lights - red and blue - one for each of my dogs.I've tried numerous dog collar lights in the past and none of them really work very well for one reason or another.The most common problems I had with other dog lights were:1. The device was of poor quality and would fall apart.2. The battery would die within a few weeks and could not be replaced.3. The device would not attach securely and would get lost in the middle of walks or while my dog was roaming about at the park.4. The light was not bright enough.Of all the dog lights I have tried, this one is by far the most effective.I installed the light on both my dogs' collars using the included velcro strap. I cut it to size and simply looped it into the grooves on the light and around my dog's collar. It is very secure. Please note that my dogs both use a flat nylon collar. This light will not work if you use a chain collar or anything that is not wide enough to secure it to.What I like about this product:1. It's waterproof. I've tested this and it actually is waterproof. Unless your dog goes open water diving, I doubt that submerging this in shallow water will ever cause any problems.2. It's bright. I keep it on blinking mode to save batteries. It can be seen from a good distance in the dark if positioned correctly on your dog's collar. Of course, there are also some limitations to visibility since the light is quite small. Hence, if you are 30-40 feet away, it's still visible but not as eye catching.3. It's got great battery life. The first one I bought is over 6 months old and still going strong. I walk my dogs primarily at night and keep the light on blink mode. On average, we walk about 1.5 to 2 miles every evening (approximately 35 mins to a little under an hour) - sometimes longer.4. It attaches securely. There's no need to keep fussing with it. Once you attach the light to your dog's collar, it pretty much stays there until you remove it.The only complaint I have about this light is the switch. The way to turn it on/off is by twisting the plastic cover of the light itself. Twisting to the right turns it on, and twisting to the left turns it off.Why only 4 stars?Although this works and is quite simple, it also presents a design flaw in that you have the tendency to twist it too much to the left when turning it off. This happened to me with one of the lights. If the light lens is too loose, it will eventually fall off. As a result, I lost one of the lights somewhere in my yard. If you're lucky enough to recover all the parts once it falls off (lens and battery), it's easy enough to put it back together and it will most likely still work. Unfortunately, with active dogs, there is no telling how much ground they cover and searching a large yard can be quite tedious. When this happened to me, I found the lens a few days after losing it but could not find the battery. Since I thought it was lost forever, I ended-up removing the device and throwing it away. A few weeks later, I found the battery but I had already thrown out the lens and the unit itself.To summarize, I would definitely recommend this light to any dog owner. I'm actually going to purchase another one to replace the one I lost. Just be careful. And, if your light comes apart, don't throw away the remaining parts as there may be a chance of you finding the parts that fell off so you can put it back together and use it again.PROS:-Bright/Easy to see (especially because it doesn't dangle under your dog's neck like traditional clip-on lights. You can put it at the back of the neck for better visibility)-Easy to attach and remove-Low chance of it falling off-WaterproofCONS:-A bit hard to twist the top and turn it on and off.Seeing as my dog is mostly dark of hair (hes a GWP), it becomes impossible to see what sort of shenanigans he's getting up to at night. So I bought this light in green because the price was right and because others said it was the brightest of all the available colors. I don't know if the latter is true, but it's definitely VERY bright! You could easily use this to be seen on walks. In fact, when I walked my dog with it on the back of his collar, it was flashing so bright into my face that I had to move it. When he's outside, I can even see it reflecting off the leaves in the trees.It is DEFINITELY waterproof. I took my dogs swimming in a lake and forgot to take it off, but it still works just as well as the day I got it (which was over a month ago).It hooks over the collar like a belt clip and seems pretty sturdy. My dog is pretty energetic, and I haven't had any issue with it coming loose or falling off. Some people said theirs came with velcro to attach it to the collar, but mine only came with the belt clip, which is fine because its easy to attach and remove. Also, you don't have to have the sort of collar that works like a belt, with a hook going into a hole. The collar I have is one that you slip on over the dogs head and then tighten to size. It doesn't have a clip or buckle of any sort, but the way this light is made you can hook it onto collars that don't open, so that is no issue.I would definitely purchase this again!I was suspicious of a dog collar light being rated for 100m depth. I’ll be darned if it actually is! Great visibility. And not a drop of water penetrated the seal at depth. Unfortunately, the dog was not so sturdy.I have a high energy black lab and he needs to go out every night. In the winter when the sun sets early I need a light on him so I (and others) can see where he is. We go to the beach and you know how labs love the water. I had bought other lights, and they lasted a few days. They'd end up getting wet, the battery would rust and they would be worthless. I found these lights and I haven't had an issue. They are waterproof, easy to put on and take off and give a decent amount of light. I put two on his collar. I haven't had any issues. He goes in the ocean and the lights keep working. These are really good lights. I bought more for a friend's dog. No issues what so ever. batteries are easy to change and are well made.This is my blinky light of choice to use on my backpacks. Compared to some of the other blinky lights, this one is very small and lightweight. Also, I’ve never had this light accidentally come off my backpack as I have with other lights when frequently picking up and setting down the bag on the ground. The plastic clip forms a little groove/hook that makes it very secure- please see the close up pix I’ve included. If this isn’t secure enough for you, it also includes a Velcro strap that can be used as an alternate mounting option which basically makes it impossible to remove without pulling the Velcro loop loose.It doesn’t have all of the different blinking modes that other lights may have but all I need is one. I’d guesstimate that this light blinks about twice a second.Second of these I’ve bought. Easy twist to tighten. Either thread it in or use the included mount. It’s actually very bright if you look straight at it. Much better then the hanging lights. Much brighter, more durable, and longer battery life. I’ve been using the first one for a year and still on first battery. I turn it on every time my dog goes outside in the dark. I live downtown so she doesn’t have much yard. She doesn’t go near the road but if she did, I want her to be seen. Without this I lose track of her in the dark because she is dark in color.Have used the light, attached with the velcro strap, to our dog's collar and with the steady light. Very pleased with the amount of vision it gives. Easy to use too and this light comes with the clip, which am yet to try. Have used it attached to running gear too and the light keeps steady as I've had similar lights which switch off, with the running action, even though I am a petite, light footed runner. Overall, the family is very pleased with this light and we think it'll have many uses.