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Shelly H&T

WiFi battery sensor, recommended default

The Shelly H&T is the recommended starting point for OpenSense. It is a self-contained WiFi sensor with a 18650 battery, a Sensirion SHT temperature / humidity sensor, and an HTTP "action" feature that can POST to an arbitrary URL on every wake-up.

We support three generations: the original (H&T), the Plus (H&T Plus) and the Gen3 (Shelly H&T Gen3). All three work with the same ingest URL; the only difference is the menu layout.

Buy

  • Manufacturer: Allterco / Shelly.
  • Price band: €25–€35 retail in the EU.
  • Where: shelly.com direct, Amazon EU, Reichelt, Conrad. Avoid third-party Aliexpress listings — counterfeits with a different (worse) sensor exist.
ok
Box says ‘Shelly H&T Gen3’ or ‘Plus H&T’ and SHT-3x sensor inside
warn
Original H&T (Gen1) — works but no longer manufactured
alarm
‘Smart H&T sensor’ with no Shelly logo. Counterfeit.

Pair

  1. Hold the side button until the LED blinks blue. The Shelly creates a setup WiFi network ShellyHT-XXXXXX.
  2. Join that network from your laptop. Open http://192.168.33.1.
  3. Internet & Security → WiFi 1. Enter your real WiFi credentials. Save.
  4. After reboot, find the new IP on your network. On Gen3 the device also exposes mDNS as shellyhtgen3-XXXXXX.local.
  5. In OpenSense, + ADD DEVICE → SHELLY → H&T. Copy the ingest URL. It is token-bearing; treat it like a password.

Configure HTTP push

On Gen1:

  • IoT settings → Reporting URL → paste the OpenSense ingest URL.
  • Reporting period → 60 s (HACCP) or 300 s (climate).

On Plus / Gen3:

  • Settings → Actions. Create a new action of type Sensor reports.
  • URL: paste the OpenSense ingest URL.
  • Method: GET (Shelly appends sensor values as query params).
  • Save.

Sample payload

Shelly does not let you change the payload format; OpenSense parses what the device sends. The format on Gen3 is:

$ shelly reports
GET /v1/ingest/shelly?token=ds_live_…&device=hut01&temp=4.2&hum=68.0&battery=3.92&signal=-58

temp is °C, hum is %RH, battery is volts on Gen3 (and percent on Gen1), signal is dBm. All five are stored. Battery and signal are auxiliary channels — they do not trigger alarms by default but are visible on the device page and useful when diagnosing offline devices.

Cadence and battery

  • 60 s cadence on a fresh 18650 → ≈ 4–6 months of battery life.
  • 300 s cadence → ≈ 18 months.
  • 900 s cadence → ≈ 36 months.

For HACCP use 60 s, period. The auditor will not accept a 15-minute gap between samples in a –18 °C freezer, and the battery cost (one swap per season) is cheap insurance.

Mount

  • Walk-in fridge: top shelf, away from the door, not taped to the evaporator. The evaporator surface is colder than the air; readings will look fine while the food rots.
  • Wall fridge / display chiller: mid-height, back wall.
  • Use Velcro or the magnetic mount accessory. Do not screw into the cabinet.

Troubleshooting

See device offline for the usual issues: deep-sleep boot time, captive-portal WiFi, MAC filtering on guest networks.

What you give up

  • The Shelly H&T cannot do dual probe. One sensor per device.
  • The original H&T does not have HTTPS — only the Plus / Gen3 do. We tolerate HTTP from Gen1 because the only payload is a small reading and the auth is via a hard-to-guess token, but we recommend Gen3 for new deployments.
  • Wake-up latency is 1.2–3.0 s on a deep-sleep cycle. If your alarm pathway is "fridge door propped open", the first reading might land after the damage. Add a Shelly motion sensor in front of the fridge for door-open detection.