Mio Sport SD Manuel D'instructions page 13

09. AutoMAtiC HeArt rAte loCk
Your MIO is not suitable for heart rate measurement during any
underwater activity (such as swimming or showering). The watch will
automatically shut down the Smart Touch sensor during these kinds
of activities in order to preserve the battery life. That means you can
still wear and use your MIO as a regular watch while underwater (see
Specifications & Limited Warranty details), but HR measurement function
will not be available until you dry your watch.
note: The watch will show the 'PLeASe DRY' screen every 10 seconds to
remind you to dry the watch.
Once your MIO is locked due to contact with water,
the DRY icon will flash to remind you to dry your
watch. This lock will be disabled automatically
once the watch is thoroughly dry. Use a towel to
gently dry the watch; do not put it into contact
with any extreme heat (such as a hair dryer).
English 10