Alarm light on my dashboard

[Cyberdyne4000]

I have a 2001 x reg 406 GLX 110 HDI. In the centre of the dashboard near to where the top meets the bottom of the windscreen is an LED. I'm certain it used to flash when the car was locked but it seems to have stopped working. The light still doesn't work even when I deadlock the car using the smaller button on the remote key fob. I've checked the alarm fuse and that is ok.
I prized out the light and it has two wires connecting it. There's no bulb to change and its in a sealed housing so unlikely to be able to prize it apart.
I've not seen another 406 with this light but its not an after market fit and I know the history of the car since new when it was bought by an elderly relative.
Does anyone else know what this light is actually for?
How is it activated?
Can it be fixed?

thanks

[Welly]

Hi, it's not actually a 'light' it is a light 'sensor'. It looks at the sunlight intensity to help the Climate Control ECU determine the cabin fan speed.

The 406's 'armed' alarm light is down by the handbrake on one of the switches (I think it's the switch that disables the interior alarm sensors).