Google has just announced Android Open Accessory which, dares us to get physical. Coming to Honeycomb and Gingerbread devices, developers will be able to tap into the accessory market like never before, making them a part of the Android experience as well. The demo showed how a USB accessory - CardioQuest could be used to monitor heartbeat while exercising.
For now, Android Open Accessory items are only supported through USB but Bluetooth support is coming soon. Ultimately, any accessory built with the ADK will be able to be plugged into your Android device and interact in many different ways, be it through an app or some other UI created specifically for that accessory. We'll have more on this soon but for now, you can check out the ADK documentation provided by Google.
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Google announces Android Open Accessory
Very very happy to see this, since this is one of the big advantages of the iOS ecosystem. I doubt handset makers will like this news though since it potentially means fewer purchasers of their overpriced garbage proprietary docks and accessories that have to be replaced with each phone upgrade.
Can't wait to have the same portability of accessories that I used to have with my iOS devices. Hopefully it also means accessory developers will be much more likely to support Android since they can target one standard interface.
If we're talking docks, speakers, etc., etc., Apple will probably continue to corner the market there, as they've made it a point to stick that huge, proprietary cable interface in the same place on every device, making "anything" essentially compatible with the next (way over-simplification).
The biggest problem with Android devices is the repositioning of the USB port on each device. While heart rate monitors and wired devices will face little obstacles, creating a dock of any sort won't allow a universal fit unless someone creates an ultra-tiny transmitter that stays put in the port, and you just rest your device in a cradle.
I'm pretty sure a wireless transmitter would not be compatible with the ADK when used with Gingerbread devices. You see, Gingerbread only supports USB host accessories, in which the accessory powers the connection, not the Android device. Since no power would be supplied from the Android USB port, the transmitter would have no power source.
However, Honeycomb 3.1 might work, because it supports USB device mode, in which the Android device powers the USB accessory/device.
"...an ultra-tiny transmitter that stays put in the port, and you just rest your device in a cradle."
http://www.google.com/search?q=define%3Abluetooth
I believe both Polar and Zephyr already have bluetooth heart rate monitors, and there is software in the Android Market to work with them.
For the sports sensor aspect, SE already supports ANT+ sensors with the X8, X10 mini, X10 mini pro and newer handsets. This means you can use Timex/Garmin/etc heart rate sensors, bicycle speed/cadence, and power sensors. The TI WiLink chipset they use enables it. No adapter needed, just a SE firmware update.
Endomondo sports tracker and google mytracks have some support, I'm just waiting to get my hands on an X10 mini, with the new models out, a used one should do the trick. Now all i need is a car battery on the back of my bike ;)