You make an impression. Not personally — who cares about that? But your body emits a thermal signature. Your breathing is loud. You smell (sorry). Your brain crackles with electricity. And it's all detectable. That's good news if you want to be rescued from a collapsed building and bad news if you're planting an IED. At least you're leaving a mark on the world.
Brain Waves
Detection range// 3 mm
Emission// Electrical activity
Signature// Amplitudes up to 200 microvolts, frequency of 1 to 30 Hz
Detection device// Electric-potential sensor
Heartbeat
Detection range// 16 inches
Emission// Electrical activity
Signature// Amplitudes mainly between 0.5 and 3 millivolts
Detection device// Electric-potential sensor
Body Heat
Detection range// 12 miles under ideal conditions
Emission// Infrared
Signature// 133 watts (average)
Detection device// Thermal-imaging camera
Breathing
Detection range// 100 feet
Emission// Sound
Signature// 10 to 25 decibels
Detection device// Parabolic microphone
Respiration
Detection range// Varies by concentration
Emission// Exhaled gases
Signature// Carbon dioxide, hydrogen sulfide, ammonia
Detection device// Gas-sensing semiconductors
Body Odor
Detection range// 50 feet
Emission// Secreted chemicals
Signature// Ammonium chloride
Detection device// Chemical-sniffing apparatus
illustration by La Boca
