You want a tight and tidy PIR sensor that is very configurable and inexpensive! Wow - check out the Zilog ePIR!
The Zilog ePIR Motion Detection Zdots Single Board Computer is a handy, tight sensor package based on PIR (passive infrared) technology. Not unlike traditional PIR sensors you find in security systems, this is designed to look for heat-motion. Unlike a security system sensor, this package is small, smart, and easy to use!
The ePIR mates a Murata lens to a Murata Pyroelectric sensor that feeds into a dedicated Z8 Encore! XP (yup, that's the full name) processor for signal conditioning & processing. The physical interface is a simple 0.1" spaced 8-pin header that's ready to be plugged into a breadboard or suitable cable. What's also particularly cool is that Zilog has also published the source code for the ePIR module, so you can see how they're using the Z8 Encore! and get a peak at the logic operations of this cool little module.
It's easy to turn the ePIR from a simple sensor module to a full serial-compatible sensor - just tie a 100k resistor to the TXD/SNS line on powerup, and you're talking to the Zilog directly via serial communications.
Manual mode: Not interested in using a microcontroller / serial interface? The pins make it easy to configure manually.
Serial Mode: Tie it to a microcontroller at 9600/N/8/1, and you get full command/response features of the ePIR. These are simple, single ASCII letter commands that let you read motion status, and read/set practically all aspects of the sensor's features, including the light gate sensor & threshold, motion status, frequency response, pulse count, and sensor sensitivity. It's pretty comprehensive!
The features of the Zilog ePIR include: