A popular fitness accessory for the iPhone is a heart rate monitor. Traditionally they have a chest strap and a matching receiver that interprets and shows the output display. Since so many people are already carrying an iPhone during exercise, using the iPhone itself as the receiving device cuts down on both size and cost. To use your iPhone as a heart rate monitor you need to purchase an adapter, a chest strap and maybe an App (if it’s not free). There are two ways the iPhone can connect to the chest strap. Either by a wireless transceiver that plugs into the iPhone or soon by Bluetooth.
The Digifit App works in conjunction with the Digifit Transceiver for iPhone. The Digifit iPhone App is free but costs around $15 if you want to use it with a chest strap monitor. Any ANT+ compatible chest strap can be used. ANT+ is a wireless fitness industry standard that many fitness brands are adopting. There are around 75 sensors that are compatible. The popular Garmin Heart Rate Monitor is one of those ANT+ compatible brands meaning it will work with the Digifit transceiver.
Runkeeper is one of the most popular iPhone apps for running. They mention on their website knowledge base, that they support one heart rate monitoring solution made by Wahoo Fitness. Wahoo Fitness is a member of the ANT+ alliance, and thus their plug-in sensor which interfaces to your iPhone will then work with any of the ANT+ chest straps. Again the Garmin chest strap would work with this solution. Interestingly Polar devices are not digital and will not work with ANT+
As far as bluetooth being used to transmit heart rate signals, there still seems to be a black hole when it comes to Bluetooth and the iPhone. Apparently Apple hasn’t opened up its software to the idea yet. There was an encouraging announcement from Nordic Semiconductor in June 2011 about the development of a Bluetooth 4 heart rate monitor strap that will work with any Blutooth 4 enabled smart phone. They’ve also developed a whole product platform similar to ANT+ which they say will give consumers an even wider choice of systems to choose from.
The App store for iPhone also has numerous Apps that utilize the iPhone microphone for measuring your heart rate, but I’m sure your first thought is the same as mine, which is how can that be accurate? And what about background noise?