Baumgartner developed its own alarm movement in mid 50's. The general idea was to develop a simple and cheap movement. Its first product was BMG 90 and even though it was simple, it was followed by an even more simple family: BMG91/902/903.  

BMG90 has two spring barrels but only one winding stem and crown. They had to prevent overwinding of one of the barrels while the second one still had to be winded. BFG90 watch can be easily recognised by two wind indicators (below 1.00 and above 5.00). While winding, indicators rotate and stop when a particular barrel is full. The upper indicator shows time and the lower one shows alarm winding status.

Instruction manual:

Crown in position 0: winding time and alarm.

Crown in position 1: Setting the time.

Bezel: by rotating the bezel one can set alarm hand.

Pusher at the left side of the case: Alarm on (down) or off (up)

BMG91/902/903 are simplified BMG90 versions. Winding indicators and On/Off pusher are removed. Bezel is not connected to the alarm hand anymore, everything is operated by the crown. In 91/902 even the second hand is omitted, however 903 still has the second hand.

Instruction manual:

Crown in position 0: Winding time and alarm (anti clockwise!). Still, one has to fully wind to be sure that alarm barrel is also full! 

Crown in position 0: Setting alarm hand by turning crown clockwise. 

Crown in position 1: Setting time.

Alarm cannot be set on/off.