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This ESP32 Wemos project is an MQTT-controlled 12 V siren output for a home-automation system. It uses separate messages to request an oscillating panic siren or a continuous fire siren, with an IRLB8721 MOSFET switching power to the sounder. It is a prototype—not a standalone, certified fire or security alarm.
What the ESP32 siren project does
Dave Wilson’s Hackster.io build, published December 28, 2019, connects an ESP32 development board to a 12 V siren and listens for MQTT messages from the author’s home-automation system. The system uses Mosquitto as its MQTT server. The board does not independently detect smoke, intrusion, or an emergency: another device or person must publish a message to trigger the sound.
The project’s three MQTT topics have distinct roles:
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| Topic | Described behavior | Status in the project |
|---|---|---|
diy/system/panic |
Requests a loud, oscillating siren. | Described as a working alarm behavior. |
diy/system/fire |
Requests a loud, continuous siren. | Described as a working alarm behavior. |
diy/system/who |
Intended for a device status update. | The author says it was still under construction. |
The topic names and behavior come from the Hackster project description. They are not a general MQTT standard; a compatible controller must publish the messages the firmware expects.
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How the hardware switches the siren
The ESP32 controls an IRLB8721 N-channel MOSFET, which acts as the switching path for the 12 V siren. The siren is not powered directly from an ESP32 GPIO. The project’s parts list specifies a 12 V, 15 W, one-tone outdoor siren and a 12 V, 2 A supply; those are listed component specifications, not independent measurements or proof that the supply suits every substitute siren.
An alternative ESP32 tutorial demonstrates a relay switching a 12 V siren and uses GPIO 16 as its example. That is a separate tutorial, not a tested replacement circuit for Wilson’s MOSFET design. Whether using a MOSFET or relay, check the sounder’s voltage and current requirements, the driver’s load and control ratings, and the power supply’s capacity before connecting components. The sources do not compare the two approaches for efficiency, reliability, or safety. See the ESP32 siren tutorial for its relay example.
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Parts in the original build
Wilson’s inventory lists the following components. Treat it as a record of this build, not a universal bill of materials: substitutions need to match the electrical requirements of the specific board, siren, and supply.
- Wemos ESP32 development board
- IRLB8721 N-channel MOSFET and a 10 kΩ resistor
- 7805 linear regulator
- Two 100 μF capacitors, two 22 μF capacitors, and three 0.1 μF capacitors
- Adafruit half-size Perma-Proto board, headers, and a 2.1 mm DC barrel jack
- 12 V, 15 W, one-tone outdoor siren and 12 V, 2 A power supply
- Electrical box enclosure
The listed tools include a soldering iron and solder, screwdriver or multitool, drill or driver, screws, and drill bits. Retail board names can be ambiguous: verify that a board is actually ESP32-based rather than an ESP8266 variant, and check the markings and revision of the particular board you intend to use.
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Prototype construction and enclosure considerations
The author first assembled the circuit on a breadboard, then soldered it onto an Adafruit half-size Perma-Proto board. The write-up describes programming and debugging the ESP32 on the protoboard and fitting the assembly into an electrical box enclosure.
The project page notes that a siren power wire remained exposed and suggests routing it through the enclosure with insulation or sealant. That is an assembly note, not a verified weatherproofing method or an electrical installation specification. Decide how to protect wiring and the enclosure based on the intended location and applicable local requirements; the cited project does not establish an approved outdoor installation method.
Rank #4
- 2.4GHz Dual Mode WiFi + Bluetooth Development Board
- Support LWIP protocol, Freertos;ESP32 is a safe, reliable, and scalable to a variety of applications
- SupportThree Modes: AP, STA, and AP+STA
- Ultra-Low power consumption, Compatible with Arduino IDE
- 1PCS 30Pin ESP32 Development Board 2.4GHz WiFi Dual Cores Microcontroller Integrated with Antenna RF Low Noise Amplifiers Filters
What this build does not establish
The project demonstrates remotely commanded sound output integrated with its author’s home automation. Calling its code “production ready” reflects the author’s characterization; it does not establish product certification, field validation, or suitability as a life-safety system.
- It is not shown to be a complete fire alarm, monitored security system, or self-contained alarm panel.
- The sources do not establish backup operation during a power or network failure, compliance with installation rules, or certification.
- No measured decibel output, current draw, response time, reliability, or comparative sounder performance is reported.
For a smoke, fire, or security system where detection, monitoring, backup power, or code compliance matters, this prototype should not be treated as a replacement for an appropriately certified system.
Best Value
- 2.4GHz Dual Mode WiFi + Bluetooth Development Board
- Ultra-Low power consumption, works perfectly with the Arduino IDE
- Support LWIP protocol, Freertos
- SupportThree Modes: AP, STA, and AP+STA
- ESP32 is a safe, reliable, and scalable to a variety of applications
Check module and component fit before building
Espressif’s ESP32-WROOM-32D/32U datasheet covers those module variants and says the series is not recommended for new designs. That does not verify that the Wemos board in Wilson’s project contains either module. Check the module markings and board revision against the relevant documentation rather than assuming the title identifies the radio module.
Before choosing substitute parts, compare the siren’s rated voltage and current, the supply’s capacity, the switching component’s ratings, the sounder’s available tone behavior, and the wiring and enclosure requirements for its location. The project’s listed components are one example, not a compatibility guarantee for other products.
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