1960's  HELBROS Gents Alarm Watch with  CAL. AS 1931 Movement
 
Brand : HELBROS 
Caliber Number : AS 1931
Movement Type : Manual wind, mechanical Diameter : 11"mm (25.6mm) 
Width : 34mm without Crown 36.5 with Crown 
Height : 50.75mm 
Jewels : 17 
Power Reserve : 46 hours 
Vibrations Per Hour : 18,000 bph 
Alarm : 12 seconds 
Features : Hours, minutes, central seconds, alarm 
Country of Manufacture :Switzerland
Production Years : 1954-1974 
 
The pictures posted here are of the HELBROS caliber AS 1931. There are two crowns. The crown at 2:00 winds the alarm. The crown at 4:00 winds the movement and sets the time. You also set the alarm hand with the crown at 4:00 by turning it counter-clockwise. Then, to activate the alarm function, you pull the 2:00 crown outpushing in to disable the alarm.
 
The AS 1931 debuted in around 1954 and was made until around 1970. The first alarm movement by the well known AS factory which delivered movements to many many makers those days. 
 
The alarm complication is its own brain in the watch. It has its own mainspring and escapement and sits adjacent to the regular gear train and regulating system. When the hour hand passes over the alarm hand it unlocks the held power of the alarm spring and sends the hammer a buzzing. This hammer vibrates against a small post that sits on the caseback and if you have sensitive teeth you may feel it in your head. These alarms on your wrist, can be quite startling.  
Gold Plated case with steel back in very good condition, dial immaculate.  
Cosmetically overall this is in very good condition and running well