Teardown and OpenBeken Configuration for DYGSM DY-SQ400B Water Leak Sensor with T1-U-HL Module

chmieleckimikolaj 01 Jan 2026 14:41 2 684 Cool? (+4)

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Hello
This is my first teardown article so please for understanding.

Introduction
I bought water leakage sensor DYGSM DY-SQ400B from Aliexpress for 1$. I wanted to connect it directly to my HA instance (bypass Internet connection requirement, which could be a bottleneck during critical situation). I flashed it with great OpenBeken (great thanks for authors

)

There is a teardown of very similar device, but with different chip (CB3S)
My device has T1-U-HL Module (BK7238) and I didn't found ready configuration on this forum neither on this website

Teardown
So I performed reverse engineering. Below is my teardown.

Pins configuration:

I created startup script autoexec.bat:

Responsibilities of my autoexec.bat:
- DeepSleep configuration for battery saving,
- configuration of faster wakeup when MQTT connection failed and water leakage is detected,
- turns on buzzer when leakage is detected (label: enableSyrena),
- turns on AP mode on reset button hold event and keeps AP mode for 60 seconds (label: apLabel),
- workaround for problem with publishing battery state when MQTT connection is established with delay (after battery measure) (label: publishBatteryState).

Home Assistant integration
I connected this sensor to my local Home Assistant instance by MQTT protocol by default OpenBeken configuration. Additionally, I created template for sensor heartbeat monitoring:

Thank to this, I can easily monitor water leakage sensor connectivity:

The red circle shows the moment of disconnection

Next steps
1. Automation to turn off the main water source pipe in case of water leakage
2. Automation to send notification in case of lack of heartbeat for specific period of time and water leakage situation

About Author

chmieleckimikolaj wrote 9 posts with rating 4 . Been with us since 2025 year.

Comments

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gulson 03 Jan 2026 11:18

Thank you! Where are you using this water leak sensor? Does he have battery power? I wonder how long the battery will last. [Read more]

chmieleckimikolaj 03 Jan 2026 13:40

I will use this sensor in my basement. Yes, it has battery slot. Battery model: CR123A Until now, I am at configuration phase, so it has stable power source. Power consumption: 30 µA during deep sleep 55... [Read more]

FAQ

TL;DR: DY-SQ400B leak sensor can be flashed with OpenBeken and integrated via MQTT; it cost $1. “I flashed it with great OpenBeken.” [Elektroda, chmieleckimikolaj, post #21795564]

Why it matters: This guide helps DIY users get local, cloud-free leak alerts and battery-friendly uptime for Home Assistant.

Quick Facts

- Hardware: DYGSM DY-SQ400B with Tuya T1-U-HL module (BK7238), reverse‑engineered pinout provided. [Elektroda, chmieleckimikolaj, post #21795564]
- Cost: Purchased for $1 on AliExpress; ideal for budget multi‑room coverage. [Elektroda, chmieleckimikolaj, post #21795564]
- Power strategy: Deep sleep with conditional wake; battery cycle set to 86,400 s (24 h). [Elektroda, chmieleckimikolaj, post #21795564]
- Buttons/LED/buzzer: Reset button triggers AP for 60 s; buzzer on Channel 2; LED on pin 28. [Elektroda, chmieleckimikolaj, post #21795564]
- HA integration: Native MQTT plus a template sensor for heartbeat monitoring and disconnect detection. [Elektroda, chmieleckimikolaj, post #21795564]

Who is this FAQ for and what problem does it solve?

For Home Assistant and OpenBeken tinkerers who want a cheap, Wi‑Fi leak sensor that works locally without Tuya cloud. It explains teardown notes, exact pin mapping, deep‑sleep scripting, MQTT setup, and a heartbeat template to catch disconnects. It targets DY‑SQ400B units with the Tuya T1‑U‑HL (BK7238) module. [Elektroda, chmieleckimikolaj, post #21795564]

What is OpenBeken in this context?

OpenBeken is an open firmware the author flashed onto the DY‑SQ400B to enable local MQTT control and custom scripts. It replaces Tuya cloud dependence and supports features like deep sleep, event handlers, and channel mapping on BK7238 devices. “I flashed it with great OpenBeken.” [Elektroda, chmieleckimikolaj, post #21795564]

What’s the exact pin mapping used for this DY‑SQ400B build?

Pins: 8=Rel;2 (buzzer), 17=DoorSnsrWSleep_nPup;1 (water input), 20=BAT_ADC;0, 21=Btn_ScriptOnly;0 (reset), 23=BAT_Relay;0, 28=WifiLED_n;0 (LED). Map these in OpenBeken’s pins config before scripting. This mapping enables sensing, sound, LED, battery readout, and button actions. [Elektroda, chmieleckimikolaj, post #21795564]

How do I enable AP mode for configuration on this sensor?

Hold the reset button to trigger AP mode for 60 seconds, then it auto‑restarts. The autoexec includes an apLabel routine: OpenAP → delay_s 60 → restart. Use that window to connect and adjust MQTT or scripts. This is useful during first setup or recovery. [Elektroda, chmieleckimikolaj, post #21795564]

How does the deep‑sleep and wake logic save battery?

The script uses DSTime and conditional PinDeepSleep to sleep when idle. It shortens wake time if MQTT failed and water is detected, prioritizing alerts. Battery cycle is set to 86,400 seconds, reducing radio use while still reporting health and voltage when online. [Elektroda, chmieleckimikolaj, post #21795564]

What statistic-based settings should I copy first?

Copy Battery_Setup 2600 3300 2 1730 4096 and Battery_cycle 86400. These calibrate voltage-to-percent and set a daily battery check. Then add addChangeHandler for Channel1 to trigger the buzzer. These values matched the author’s working unit and logs. [Elektroda, chmieleckimikolaj, post #21795564]

How do I integrate the sensor with Home Assistant via MQTT?

Use OpenBeken’s default MQTT. Then add the provided template sensor listening to topic water1/host to record a timestamp and readable date on each message. This acts as a heartbeat to spot gaps when the device disconnects. [Elektroda, chmieleckimikolaj, post #21795564]

What’s an easy 3‑step setup to replicate this build?

Flash OpenBeken on the DY‑SQ400B (T1‑U‑HL/BK7238) and set Wi‑Fi/MQTT.
Apply the exact pin map, then paste the autoexec.bat script.
In Home Assistant, add the MQTT template sensor for heartbeat monitoring. [Elektroda, chmieleckimikolaj, post #21795564]

How does the buzzer alert get triggered on leak?

Channel 1 is the water sensor; Channel 2 drives the buzzer (alias enableSyrena). A change handler addChangeHandler Channel1 == 1 enableSyrena turns the buzzer on when leakage is detected, ensuring an audible alert immediately. [Elektroda, chmieleckimikolaj, post #21795564]

What is Tuya T1‑U‑HL (BK7238) in simple terms?

It’s a Tuya Wi‑Fi module using BK7238 that powers the sensor. OpenBeken supports it, enabling direct MQTT and custom scripts. In this teardown, it replaced a CB3S‑based approach seen in similar devices, while delivering the same local‑control outcome. [Elektroda, chmieleckimikolaj, post #21795564]

How do I publish battery voltage and percent reliably?

The script waits for MQTTState 1, then publishes voltage and battery level in a publishBatteryState label. This avoids missing battery updates when the broker connects after measurement. It’s a targeted fix for delayed MQTT sessions. [Elektroda, chmieleckimikolaj, post #21795564]

What edge cases should I expect with MQTT connectivity?

If MQTT connects slowly, battery telemetry may fail to publish without the added waitFor MQTTState 1 logic. The script also accelerates wake when MQTT fails and water is detected, reducing time‑to‑alert during outages. “Faster wakeup when MQTT connection failed.” [Elektroda, chmieleckimikolaj, post #21795564]

Can I detect when the sensor goes offline in Home Assistant?

Yes. The MQTT template writes the current epoch on each message. Plotting the value reveals gaps; a red circle in the author’s chart marks a disconnect. Use automations to alert if no heartbeat arrives within your chosen interval. [Elektroda, chmieleckimikolaj, post #21795564]

How should I plan next automations?

Create an automation to close the main water valve on leak detection. Add another to notify when heartbeat is missing for a set time, especially during an active leak. These were the author’s stated next steps. [Elektroda, chmieleckimikolaj, post #21795564]

What’s the best naming and channel strategy?

Use SetChannelLabel 1 Wyciek (Leak) and 2 Syrena (Buzzer). SetChannelType 1 OpenClosed_Inv for clear HA semantics. This keeps dashboards readable and scripts maintainable while matching the device’s behavior. [Elektroda, chmieleckimikolaj, post #21795564]

How do I keep configuration access without opening the device?

Hold the reset button to start AP mode for 60 seconds, then the device restarts. Use that window to adjust MQTT, Wi‑Fi, or scripts without disassembly. This behavior is baked into the autoexec’s apLabel routine. [Elektroda, chmieleckimikolaj, post #21795564]