AVer SF2111H-DVR user manual - Manual (Page 13)

9
4. I/O Interface
I/O Connection
a. Please connect the GND & DO pin to the external relay (buzzer) device.
b. Please connect the GND & DI pin to the external trigger device.
c. I/O PIN definition
GND (Ground): Initial state is LOW
DO (Digital Output): DC 5V
DI (Digital Input): Max. 50mA, DC 5V