Ramesh, site supervisor
Types his crew in Hindi. At 7 pm gets tomorrow's plan: stop 9 to 5, rest bands, 7 water cans, as text and a voice note. Approve saves it to the record.
A guard for the heat you cannot see.
Pehra turns the free forecast into WBGT work-rest plans in Hindi, on WhatsApp. No app to install.
40 log, 10 bhaari kaam
Kaam band: 9 se 5 baje
paani Connaught Place
Peene ka paani: 190 m
India warns with a thermometer. Bodies break from heat and humidity together.
4,372city-days over the WBGT work limit with no heatwave declared, in 12 cities, 2021 to 2025
2,327of them outside March to June, when heatwave bulletins do not run
38.8 °CKharghar, 16 April 2023: no heatwave under the rule, yet WBGT in the sun reached 30.8 °C against a 28.2 °C limit
ERA5 reanalysis via Open-Meteo. The IMD rule is recreated, not IMD's record. Counts are minimums. Read the audit and the model card.
Four people, one guard. Recorded on a real phone.
Gurpreet, worker
Scans the site QR. No app, no login. Logs a rest break. Taps chakkar if dizzy: fixed first aid for him, a WhatsApp alert and a Hindi call for Ramesh.
Meena, expecting
Five button questions about the household, counts only. Today's plan uses stricter limits for the vulnerable. On dangerous days Dadi gets a Hindi phone call.
Lakshmi, vendor
Types paani, Connaught Place. The nearest drinking water is 190 m away, with a map link, from OpenStreetMap and community reports.
WhatsApp test number and a Twilio trial call, recorded on 11 October 2026. The people are illustrated; the messages are real.
For sites with no smartphone, Pehra is a box.
About ₹600 of parts around an ESP32. It measures the real WBGT on the site, acts on it, and talks to AWS IoT Core. Every box gets a live 3D twin.
DHT22
Air temperature and humidity: the wet-bulb part of WBGT.
Black globe probe
Radiant heat from the sun, tin roofs and concrete: the globe part.
Two sonar sensors
Drinking-water tank level and drain level: refill, and waterlogging alerts.
Ring, siren, relays, SOS
Risk colour, a rest bell every hour, a mist fan, a tank pump, and a red button that calls the supervisor.
What happened on 11 October
Readings published to IoT Core: WBGT 34.2 °C, khatarnak, tank 17%. The pump started, WhatsApp got two alerts, the twin went red on SOS, and the phone rang in Hindi.
Firmware and wiringThe six-minute demo
How it runs
- Forecast to WBGT, once per city. EventBridge runs a Lambda three times a day; Open-Meteo in, WBGT out to S3. A million sites cost the same as one.
- Plan, approve, send. WhatsApp hits API Gateway and a Lambda; Step Functions waits up to 12 hours for the supervisor's Approve; SQS rate-limits the sends; Polly speaks the Hindi.
- AI explains, policy guards. Amazon Bedrock with Strands Agents writes the explanation; every number comes from tools; Cedar makes sure the AI can never loosen a limit.
- Devices and records. IoT Core takes the Site Box readings over X.509 MQTT; DynamoDB holds sites, people and boxes; each day's record is hash-chained in S3 Object Lock.
One SAM stack in ap-south-1 (Mumbai). Source on GitHub, 246 tests.
What Pehra does not claim
It does not save lives and it is not medical advice. It is designed to reduce exposure. Every number it sends comes from code, never from the model.
