Sometimes accelerometers and GPS just aren’t enough. Digifit iCardio offers a free App (with in-app purchases) that not only has accelerometers and GPS but also offers access to information from a heart rate monitor! Available for iOS and Android, you can pair it with any supported heart rate monitor to track yourself during your workouts. Reviews show great accuracy when it comes to judging heart rate, but be aware that the set-up can get costly with all the add-ons. Another great thing about this app is just how customisable it is, you can choose how often and in what ways it alerts you about your goals. Whether you prefer vibration after each mile or a voice in your headphones at periodic time intervals, you choose the information you want to receive.