For runners, one of the biggest headaches of buying shoes is knowing when it's time to replace your old ones. No one wants to plop down cash for a new pair prematurely, but at the same time, running in a pair that has seen better days can lead to serious discomfort and injury.

The consensus is that it's a good idea to replace your running shoes every 300 to 500 miles, Huffington Post notes. But unless you're diligently keeping track of your mileage, it can be difficult to notice the signs of a worn out pair.

Oftentimes, a sneaker's outer traction may appear to have plenty of grip left, but its inner cushioning may be flattened and ineffective. Likewise, just because a pair still feels comfortable doesn't always mean it's safe for the road.  

Enter Mino, a wearable gadget that tells you the exact moment you should replace your runners. By using a microchip that tracks your number of steps and the amount of pressure placed on the footbed, Mino notifies the wearer at around 400 miles that it's time for an upgrade. This eliminates the uncertainty factor and ensures runners get the most out of their kicks. 

The best part is that a pair of Minos costs just $15. Check it out in action below and visit their website for more information.