I'm not sure what wireless standard Sigma uses, but the two that seem to be emerging are low power Bluetooth (BT 4.0 or BT LE) and ANT+.
The interesting thing is that many sensors are now coming out that support BOTH standards. Wahoo Fitness has a number of sensors that simultaneously put out BT LE and ANT+ signals. So, for example, I was able to run my Garmin Edge 1000 on the bars as the same time my iPhone 6 running Cyclemeter and have them take the same data. The Edge 1000 takes ANT+ and the iPhone can connect to BT LE. One sensor fed both bike computers.
Incidentally, the same is true for Wahoo Fitnesses magnet-less cadence sensor, their HRM. Also my MIO Heart rate monitor does the same.
Then there is this syncing service: https://tapiriik.com
This takes a number of services - Garmin Connect, Dropbox, Strava, Runkeeper, etc... and syncs between them. I can take my gamin unit have it automatically upload at the end of a ride and it will sync the data between Strava and my Dropbox account where I can then import into Cyclemeter. The reverse also true.