Yes, you can connect any type of NC (normally closed) contact to the extra input on the DS90 (e.g. smoke detectors with a NC relay contact). The extra alarm contact has its own zone number on the console. 

Wired sensors that are connected to the external ins of the system behave in the same way as a DS90 door/window sensor. 

Yes, you can connect any type of NC (normally closed) contact to the extra input on the DS90 (e.g. smoke detectors with a NC relay contact). The extra alarm contact has its own zone number on the console. 

One of the sensors or motion detectors has not contacted the base console for a long period of time. Check the batteries in the sensor or motion detector. Erase the zone and reregister the sensor. Move the sensor so that the signal can reach the console. If an error is found while setting the alarm, you will hear a repeated two-tone ‘error signal’. If a sensor indicates a problem (e.g. an open window), you can decide not to activate this sensor.
You need to press CLEAR while the error message is shown and then activate the alarm again. The zone indicator of the sensor concerned will now flash quickly.

You have pressed the CLEAR button to activate the security system while a sensor or motion detector has indicated a problem. Solve the problem (i.e. close the window, replace the batteries) before activating the zone.