IR movement detector

Might be a little difficult to do.
IR detectors work on a loop system, thus the need for a reflector.
The transmitted beam is sent out to be reflected by the "reflector" and received back at the transmitter. If this "Loop" is broken the circuit changes state and activates whatever you need.
You maybe looking for a movement sensor utilising microwave signals. However the rest of the detection area needs to remain still.
Or another device detects changes in volume of air from a single point. These maybe available from J@yC@r, and sense a start volume of air in the immediate area, and any large changes of air volume trigger the device. Useful for car alarms as an extra device to detect such things as broken windows letting more or less air into the car, or if the door switch have been bypassed and entry is gained to the car, then "Volumator" detects changes, with the 80 -90 Kgs of mass that just entered the car.
Jas> Hi guys,

"Jason S" while reading the NewsGroups, found courage and express out opinion in news:4279f99d$1 snipped-for-privacy@news.iprimus.com.au:
An optical mouse is a motion detector. It is very small and would work with reflected light source. I don't know if it would work with IR though.
Par.

Y'know, I've never had luck getting my optical mouse to work when pointing it at a wall 5 metres away. -mark

"Jason S" ** Normal IR movement detectors do not work like that at all.
Please explain the application and principle of operation you envisage.
............. Phil

Ok, haha, maybe I'm asking too much. But this is the situation:
I want to hide a motion detector of some sort that could "see" between a small gap... probably around 10mm wide. I want something small enough to "spy" a little through the gap. That's why I was thinking ultrasonic detectors (which didn't work as well as I expected), or IR LED system. But if I need a reflector, then its useless. You see, I don't want this detection system to be seen (as it would give away a little secret of mine, haha). By the way, I just realised it doesn't need to be 5 metres. Even 2 metres would be enough in my situation.
An invisible but narrow beam is what I probably need. I found that ultrasonics don't trigger as easily through a gap.
Thanks.

"Jason S" ** Obviously a mail box slot.
** A video camera will do that.
** A video camera and a circuit monitoring the output signal to detect a *sudden* change in the light level or scene.
.............. Phil

No, I just want it to trigger a circuit to alert me someone is there. I dont want to use a camera of any sort. There is no need. But I don't want this movement detector to be seen. Actually, this would be hidden in the gap between an open door and its frame!

"Jason S" "Phil Allison" ** Just what the camera will do - trigger an alarm when the video signal undergoes a sudden change due to someone standing in or moving past its normal view.
** You have no bloody idea what is needed and there is no simpler alternative.
** Do you have a clue how small video cameras are ??
Less than match box size is common.
** Easily done with a mini camera.
............. Phil

thank you.

Thats not really detecting movement?
How about a Sharp IR ranger? The GP2Y3A003K0F is 400mm to 3000mm range, detect a thresholded change of distance measured through gap as the trigger.
Don't know why you'd need 5 or even two meters if its between open door and frame.... (Refer to other ranges of Sharp IR sensors here :

"Mark H" while reading the NewsGroups, found courage and express out opinion in news:427aea63$ snipped-for-privacy@duster.adelaide.on.net:
BUgger your foolish comment.
If you have half a clue, you would know that an optical mouse is actually a small video camera of very small pixel count. It detects the changes in light level and movement of the changes.
You would have to change the lens though. The one that came with the mouse is focusing at 1 - 2 mm away (thats why you dont have luck with walls 5 meters away) try the lens from an old disposable camera to focus at the mouse's ccd.
(see Phil Allison's post of the same principal... This is strange, I am agreeing with Phil...)
Par.

How about a PIR sensor. The RE200B from Nippon Ceramic Co. This assumes human body detection. Here is more info on a kit:
and also the raw device: