It is recommended that you use something that is louder than the speaker on your device. You want to make sure you don't miss an alert, or have a hard time hearing the alert coming from your device. Below I have listed devices either I have used personally, or know someone else who has used it. I tend to not always stick with main stream products, I like to find new and upcoming products from newer and more low key companies. So I hope this list will be helpful to anyone out there looking for a way to enhance their devices audio!
Outdoor Tech Buckshot Pro
You can use any device that has audio, however I recommend something built to be loud and take the abuse of being on the trail.
My personal favorite device for volume is the Outdoor Tech® Buckshot Pro.
Not only is it loud, and a device charger, it also intergrates with your device to help you hear/answer incoming calls, text messages etc. I have had mine for almost two years now, and I have not been nice to it at all. I have subjected it to tempatures over 100°F, and plenty of time in sub-zero tempatures when fat biking in the winter time. And this thing will not quit! I have yet to have the battery die, even when using Chasing Your Trail along with listening to music at high volume for hours on end. I have crashed multiple times with the Buckshot Pro on my handlebars, and it just keeps on working. Very happy with this device, so I have to recommend it!
If you wear a helment, and you don't like having earphones stuck in your ears, then you'll love the O-Tus Bluetooth speakers! They mount right onto your helmet along with the Bluetooth device. The speakers point slightly towards your ears to direct the sound to help you ear your audio better.
I love how simple and portable this device setup is. You just place the adhesive velcro pads on each side of your helmet, and then stick the speakers to them. This way you can use the speakers on more than just one helmet.
The only recommendation I have is when mounting the adhesive velcro pads onto your helmet, is to use something like Gorilla Glue to make sure the pads never come off. I'm not very nice with my stuff, and tend to throw my helmet around more than I should...and this would tend to rip the speaker pads off my helmet. After I glued them in place, they haven't come off since!
The Broski Bluetooth Sports Earphones fit snuggly into your ear, don't pop out as you move, and have great sound! These earphones are great for any kind of activity. They are easy to setup, and easy to use!