Module

Model: M150 (for Men's calculator watch)
Battery: 391 Face: LCD 8 digit + week + alarm  Light: YES Year: 1980 Buttons: Four buttons are used: top right, bottom right, top left, and bottom left.
Function: It displays hours, minutes, seconds, day, and month, as well as alarm and buzzer functions. It also has a built-in calculator. It also features a built-in light.
Info: This module is used in the following model TI-810-21 

 
Here you can see the specific contact used by the button when pressed. Four buttons are used: one in the top right, one in the bottom right, one in the top left, and one in the bottom right. The top right button allows you to select the time, date, and seconds; the top left button activates the backlight via the internal micro bulb; the bottom left button allows you to set the time, date, day of the week, alarm, and calculator; and the bottom right button allows you to change the time, date, and alarm.

 In this one you can see the micro buzzer on the inside of the watch case cover.