Not a listen to your heart thing or tap on the screen when you feel your pulse thing, but one that works with a chest strap etc…?

sort of…

http://smheartlink.com/faq.html

Apparently the iphone has ANT connectivity built in (how the Nike sensors connect to the phone, and how other brands of HRM communicate – e.g. Polar, Garmin etc…) but it's not available to app developers, so there are no apps that can just take a signal from an ANT transmitter and do anything with it…

Thats a real shame. Would get round the ~Polar hates Mac issue I'm suffering at the moment.

there's now a Polar Bluetooth wearlink that works with Nokia phones, not sure if there's work going on for the iphone though

Polar's aren't ANT+ anyway, although Garmin, PowerTap, SRM etc are. Didn't know the iPhone was, that's very clever.

I'm not 100% sure what the Nike+ kit is, I thought it was a custom protocol, in the same frequency as Bluetooth, ANT or XBee, but I think not the same protocol. Wikipedia says that it is ANT, but looking at it, there isn't any evidence for that, and the fact no one has got it talking to other devices suggests it isn't ANT (and the fact the Nike+ units don't appear to talk nicely with a standard ANT receiver).

Oh actually a little digging, and it appears that it is a non-standard protocol, so no luck there.

What you need is an external receiver – there is one I know of:

http://en.pedalbrain.com/pricing

These people have an external ANT transmitter that talks to things like powertap hubs and suunto heart rate monitor straps and all that gubbins.

Not cheap mind, $200 for the bit to connect to the iPhone, plus a subscription that you have to pay to use it.

Or a bluetooth heart rate strap. There are a few of these, but they are all either very expensive medical things, custom built, or the Nokia thing, which is not possible to buy separately, and probably locks itself to only talk to Nokia phones.

Joe