How JagaMata estimates your child's face distance

JagaMata has no special distance sensor. It uses something every phone already has: the front camera. This article explains what actually sits behind the "cm" number on the home screen, and why calibration makes a difference.

A closer face looks bigger

The principle is simple. The closer a face is to the camera, the bigger it appears in the frame. The Google ML Kit face detector bundled in the app finds the face in each frame and draws a box around it. JagaMata reads the width of that box as a fraction of the frame width, for example a face filling 40% of the frame.

When the face moves twice as far away, its width in the frame roughly halves. That inverse relationship is what gets turned into a centimetre estimate.

Why calibration matters

A 4-year-old's face is smaller than a 10-year-old's. Without calibration, JagaMata uses a default value, and a child with a smaller face will appear further away than they really are.

Calibration fixes that. You start it from the child's profile with Distance Monitoring switched on (calibration needs the camera); distance warnings pause while you calibrate. You ask your child to sit 30 cm from the screen, facing the camera, then at 50 cm, and JagaMata records the face width at both distances. With those two points, the app fits an estimate line specific to that child's face. The second reading must be clearly smaller than the first; if your child hasn't actually moved back, the calibration is rejected and you're asked to try again.

All that is stored is two fractions. No photos, and the numbers cannot be used to identify anyone.

Sensitivity: how long before the screen dims

A face that leans in briefly to look at something shouldn't be punished straight away. The Sensitivity setting decides how long a face must stay too close before the screen dims: 1 second (high), 2 seconds (normal) or 3 seconds (low).

Tips for the best results

• Calibrate in good light. The face detector works better when the face is clearly visible.
• Recalibrate as your child grows, or when they start wearing glasses.
• Use a separate profile for each child (a Premium feature) so each one has their own calibration.
• Remember this is an estimate, not a medical measurement. The goal is building better distance habits, not replacing eye check-ups.