This applies to all Network Cameras with an Alarm Out.
The Alarm Output connection on modern Network Cameras is not a contact closure but a voltage level change.
Below, please find a diagram of the circuit needed to create a relay operated closure.
Alarm Out Wiring
An easier solution would be to utilise a ready made relay module available in many versions similar to the ones below pictured
Besides the relay module, a DC power-supply may also be needed