A lie detector test, also called a polygraph test, works by measuring your body's involuntary physical responses to questions — based on the idea that lying causes stress and stress changes your body’s signals.
🧠🩺 How It Works: Step by Step
1. Sensors Are Attached to You
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Around chest and abdomen – to track breathing rate
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On fingers or palms – to monitor sweat (skin conductivity)
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Around arm – to measure blood pressure and heart rate
2. Baseline Is Set
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The examiner asks simple, known-truth questions (like “Is your name Kannan?”) to see what your normal body reactions look like.
3. Critical Questions Are Asked
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Some questions are designed to test truthfulness (e.g., “Did you take the money?”).
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Your body’s responses are compared to the baseline.
4. Interpretation
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If your heart rate spikes, breathing changes, and palms sweat abnormally, it may suggest stress or deception.
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The examiner interprets the data from the polygraph chart.
📊 What It Measures:
| Signal | What It Shows |
|---|---|
| Heart rate | Increases with stress or fear |
| Breathing rate | May become shallow or irregular |
| Blood pressure | Often rises under tension |
| Skin conductivity (GSR) | Sweat increases electrical activity |
❓ But Does It Really Work?
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Not 100% reliable
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People can be nervous even when telling the truth.
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Trained liars or sociopaths may suppress their reactions.
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Some try tricks like biting the tongue or controlling breath.
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Courts in many countries (including India and the US) often do not accept lie detector results as sole evidence.
🧪 Analogy:
A polygraph is like a stress detector, not a truth detector.
If someone shows signs of stress when answering a question, it might mean they’re lying — but it could also mean they’re just scared.