Passive (default) mode
Trap detection radius: 3.33m (~11ft)
Trap detection rate: 6 seconds (every round)
Trap detection roll: d20 + full skill (in version 1.68, probably a bug)
Spot/listen roll: d10 + half skill
Active (detect) mode
Trap detection radius: 6.66m (~22ft)
Trap detection rate: 3 seconds (twice per round)
Trap detection roll: d20 + full skill
Spot/listen roll: d20 + full skill
Stealth checks
Player detects stealth: 5 times per second
Player rolls for hide/move silently/spot/listen: 6 seconds
NPC detects stealth: 4 seconds
NPC rolls for hide/move silently/spot/listen: 6 seconds
All I could find..
http://nwn.wikia.com/wiki/Detect