Unfortunately, I have to adjust the chest strap before each run. Runtastic app settings, heart rate measurement. Then, the belt is not detected. Bluetooth off, then on again. Then it will be recognized. Mostly, do not always ... And this procedure each morning.
Conclusion: S4 on the strap under Android 4.2 was great, since the update to 4.3 only moderately, see above. on the S3 the belt under 4.2 was not, since the update to Android 4.3 standard as the S. 4
So no absolute recommendation for this configuration.
Addendum: - no more fumbling now also connect to the laborious work of bluetooth / bluetooth from / bluetooth. When a connection ever comes about, incorrect values are transmitted. In idle state, for example, 69, while running 34 or even 49 times ...
Conclusion: The part is in any case unusable with Samsung S3 and S4 under Android 4.3. Definitely not buy recommendation.