The Human Sensor
A sensor is a device that turns something from the world into a number. And you can be a sensor too! This lesson is completely screen-free: you will measure, write on a sheet and decide what to do.
For parents: a one-page guide — dinner questions and a round without a screen.
01Remember
Think first, then open the answer.
What is a sensor?
A device that notices something in the world — light, heat, sound — and turns it into a number. A thermometer is a sensor for heat.
What do we use to measure how warm it is?
A thermometer. It shows a number in degrees Celsius (°C).
Where is it usually cooler — in the sun or in the shade?
In the shade. That is why we do not put a thermometer in direct sunlight: it would show more than the air around it.
02Story
In 1742, the Swedish astronomer Anders Celsius came up with a scale for temperature. He used two easy points: when water boils and when ice melts.
His first scale was upside down! Boiling water was 0 and melting ice was 100. Soon afterwards, scientists turned it around and got the scale we use today: 0 for ice and 100 for boiling water.
The name “Celsius” honours him. So when you write °C in your table, you carry on an old story of people who wanted to compare numbers.
A sensor measures just one thing. You notice many things at once. How do you know it is time for you to rest?
03Worked example
Mimi is an invented girl. On Sunday evening, while the family watches TV, she is a “human noise sensor”. Here is the path from a number to an action:
Measure
She listens and rates the noise with her ears on a scale from 1 to 5. She decides: 4 — you have to raise your voice to hear each other.
Record
In the table, in the row “Sunday · evening”, she writes 4.
Understand
She sees that on the earlier evenings the number was 2 and 3. So tonight is noisier than usual.
Act
She asks them to turn the TV down. Next time she listens again and writes a new number. That is how you see whether it helped.
The numbers in the example are invented, for learning only.
04Try it now: the measuring sheet
My “Human Sensor” sheet
Measure in the same place and at the same time. Keep the thermometer away from sun, stoves and radiators. Wait a few minutes before you read the number.
| When | Where (room) | Degrees °C | Noise 1–5 | Aired ✓ | Drank water ✓ |
|---|---|---|---|---|---|
| Day 1 · morning | |||||
| Day 1 · noon | |||||
| Day 1 · evening | |||||
| Day 2 · morning | |||||
| Day 2 · noon | |||||
| Day 2 · evening | |||||
| Day 3 · morning | |||||
| Day 3 · noon | |||||
| Day 3 · evening |
Noise by ear: 1 — very quiet · 2 — a quiet chat · 3 — normal talking or TV · 4 — noisy, you have to raise your voice · 5 — very noisy. This is your ears, not an exact device. If the noise bothers you — move away and tell an adult.
Aired: put a ✓ if a window was open during the last hour (opened with an adult).
My discovery: it was warmest in ……………………… · it was noisiest in ………………………
I will: ……………………………………………………………………
A learning measurement. Not an official check and not medical advice. No names or addresses on the sheet. · Children's Library · East Accelerator Foundation · kagami.bg/en/deca
05No screen: a round for the family
The whole lesson is screen-free, but this part is for everyone together. You need the sheet, a pencil and at least one more person (in class — a team of four).
Share out the roles: Thermometer — reads the number; Ears — rates the noise from 1 to 5; Window — with an adult's agreement, opens it and writes down when the room was aired; Jug — reminds everyone to have some water if they are thirsty. Swap roles every day.
Three times a day (morning, noon, evening) you walk through the same room for two minutes and write on the sheet.
On the third evening, put the sheets side by side. Where are the numbers higher? When is it noisiest? Did it get better after airing?
Choose one action for the next days: for example “we air the room before dinner” or “the TV is quieter”. After three days, measure again and compare.
06Make your own
Turn the numbers into a picture.
- On squared paper, draw a bar for each temperature measurement — a higher number, a taller bar.
- Invent your own column: something else you can rate without a device, for example “how bright it is” on a scale of 1–5. Add it to the table.
- Show the sheet to someone at home and tell them one thing you found out.
07What I learned
- A sensor turns something from the world into a number. You can be a sensor too.
- A number alone is not enough: I record it, I understand it and I act — I air the room, I drink water, I lower the noise.
- We measure in the same place at the same time, so we can compare.
If something scares you — tell an adult you trust.
Check yourself
1. What does a sensor do?
2. You rated the noise 5 — very noisy. What is a good thing to do?
3. Where do you put the thermometer?
It is yours when you have a filled-in sheet and can say what you did with the numbers. No points and no rankings — just a skill.
08I have a question
Do you still have a question? Write it here. It goes to your parent, not to strangers. Your parent confirms their e-mail first.
The form is loading… If it does not appear, write your question on paper and show it to a parent or teacher.
·Sources
- Title: The Human Sensor (DB-IS-04) · Author: Children's Library, East Accelerator Foundation · Source: original content, 2026 · Rights: CC BY-SA 4.0.
- Facts about the Celsius scale: Wikipedia, “Celsius” (read on 01.10.2026) — only the facts were used, the text was not copied.
- School link: Bulgarian curriculum “Man and Nature”, grade 5 (in Bulgarian) — measures temperature with a thermometer and presents results in a table (read on 01.10.2026).
- The measurements in this lesson are for learning. They are not an official check and not medical advice.
- Licence: CC BY-SA 4.0 · Children's Library, East Accelerator Foundation, 2026. You may share and adapt this lesson if you credit the author and keep the same licence. Learning is free forever.