Q-See QSD2316L User Manual page 16

Alarm output:
The DVR has 4 channel relay alarm output, which just gives on/off signal to external alarm. The status of these
pin are illustrated as 8.
Before alarm
10
Digital Video Recorder User Manual
Fig 2.7 Sensor Connection
After alarm
. .
N O
COM
. .
N C
Fig 2.8 Relay Output Status
. .
N O
COM
. .
N C