Alcad ACO-000 Manual Del Usuario página 13

VIDEODOOR ENTRY SYSTEMS
CONNECTION OF THE AUXILIARY PUSH-BUTTONS
The PC interface has 4 connection terminals which correspond to the F7 and F8 keys on the keyboard of your PC (see illustration below).
Applications: control of additional elements.
Important:
Terminals number 24, 25, 26 and 27 are potential-free contacts. To use them, take into account the following connection limitations:
50 mA 12 Vdc.