PIR switch issues

[compton]

Hi,
I am having problems with PIR switches. I am not sure if I am doing something wrong or I misunderstood how they work. I installed one in the ceiling of a 4x2m storage room. When I walk under the detector, the light switches on as intended, but it turns off shortly after with me in the room. Changing the time settings in the sensor will just delay the moment the lights go off even with me inside. I thought PIR sensors would detect my presence and only turn off once I am out of the room??
Is this an issue or is this how they are supposed to work??. I have had the same issues with two of them. One was a very cheap one from eBay, so I was not surprised it would not work. The last one is a recessed installation one from Screwfix, so I start to wonder if I am doing something wrong?
Thanks!

 

[EFLImpudence]

That's how they work.

They detect movement, not your presence.
Is there also a sensitivity setting as well as time?

Keep waving your arms around.

 

[compton]

There are two settings. One for time and one with a light bulb, which I had assumed was so that it only lights up when is dark. I cannot see a sensitivity one.
I suppose I will have to get used at waving...
Thanks