Radar-based human presence detection for security

The problem

A traditional PIR sensor only detects heat changes during movement: if someone walks in and stands still, the sensor considers them gone and stops the alarm. It's also fooled by sunlight and AC drafts, and can't see behind any cover. The result is a security system that gives frequent false alarms and gets switched off, or misses someone moving slowly. Radar measures distance itself, so a still body stays visible to it — it can even detect breathing.

How it works

1. ScanningThe radar emits millimeter waves and continuously measures the reflection's return time.
2. RecognitionThe radar tells moving targets from still ones, and calculates their distance and angle.
3. ZoningThe room is divided into zones, each with its own sensitivity and behavior.
4. ConfirmationWhen a target enters a restricted zone, the camera takes a photo for visual confirmation.
5. AlertsAn instant local alarm, plus a notification with the photo and distance in the owner's app.
6. RegistrationEvery event is saved in a time log with its position in the room.

Project features

• It detects a still person — exactly where all PIR systems fail.
• It passes through curtains and thin wood, and needs no direct line of sight.
• It determines distance and direction, so you know where the intrusion is, not just that it happened.
• It only takes photos when a real event happens — better for privacy than a camera running around the clock.
• It relies on relatively new technology, rarely used in graduation projects.

Expected challenges

These are the main obstacles to expect during the build, laid out clearly so you know them before you start.

• Tuning sensitivity: the radar is sensitive enough to pick up a curtain moving in a draft.
• Reflections off metal surfaces create phantom targets, so filtering and exclusion zones are needed.
• The mounting position is decisive: the angle and height set the whole coverage area.
• Telling a person from a pet needs extra logic based on the target's size and height.
• Data from a system watching inside a home must be encrypted and stored locally for privacy.

The consultation gives you a solution for each one.

Expected committee questions

Prepare your answers in advance: these questions come up often in defenses of similar projects.

1. How can millimeter-wave radar detect a person standing completely still?
2. How is a person told apart from an animal or a running fan?
3. What advantages does radar have over a camera or PIR sensor in privacy and accuracy?
4. How was the space divided into zones, and how are false alarms reduced?

Practice the defense, question by question