Beurer SL 40 Instructions For Use Manual page 31

3 Switching on the control unit
To switch on the anti snore belt, press and hold the ON/OFF button
on the control unit. An LED will begin to glow blue. If an LED
flashes red three times, you must charge the control unit battery. To
do this, follow the instructions from chapter "Charging the battery",
on page 29.
31