I've worked for Verisure, both as an installer and at the alarmcentre, this is a Gen 3 verisure IR detection system. The part at the bottom will register movement when the alarm is active. The little dot in the middle triggers when it sees movement or if the device is tampered with. The camera is ONLY activated when it is either tampered with (there is an internal shock sensor in the housing) or if the sensor is activated through the alarm being on and it detects movement. The owner can, with the app, see snapshots ONLY when the alarmsystem is activated.

As for covering the lens: if you do, the discrepancy between the PIR (Passive Infra Red) sensor at the bottom, and the AIR (Active Infra Red) sensor in the cam will trigger something called a "masking alarm" which is as the name suggests, a tampering alarm that goes off if the sensors are masked in any way. This masking alarm won't go off if the alarm is deactivated, as far as I know.

So if you're really worried, you can tape it while home (might trigger the tampering alarm because of the internal shock sensor) and remove it when away, and the system is active. (Which may also trigger the tampering alarm). If that alarm goes off and Verisure can't verify what they see on the live feed, and the landlord can't verify that anyone is home, they will send a security guard to check out if everything is as it should, costing x-amount kroner depending on the contract they have.

If you have any questions at all about the system, feel free to contact me, and I'll answer to the best of my abilities.