🔥 Your Goal

You want to know when a tenant leaves a stove on, or detect if there’s an open flame / fire, to reduce fire risk.

There are a few inexpensive sensing options depending on how you want to detect it:

🧭 1. 

Flame Sensors (Infrared / UV)

• How it works: Detects the light signature (UV or IR) of an open flame.
• Pros: Directly detects actual flame — fast and simple.
• Cons: Must “see” the flame (line of sight).
• Cost: around $2–$20 (very cheap).
  Examples:
  
• YG1006 or IR flame sensor modules (Arduino compatible).
• UVTron flame sensors (around $10–$30, higher sensitivity).
• 
  

💡 Use case: Works well if you can place the sensor near the stove with clear line of sight to the burner.

🌡️ 2. 

Temperature Sensors

• How it works: Measures the heat of the area or object.
• Options:
  
• Thermistor / DHT11 / DS18B20 sensors: Cheap ($1–$5), detect local temperature rise.
• IR thermopile sensors (like MLX90614): Detect surface temperature without contact, $10–$20.
• 
  
• Pros: Can sense if a stove is hot even if the flame isn’t visible.
• Cons: Might not detect gas flame if nothing is heated yet.

💡 Use case: Detect if the stove or cooktop stays hot too long.

🧪 3. 

Gas Sensors (for Gas Stoves)

• How it works: Detects unburned gas or combustion byproducts.
• Options:
  
• MQ-2 / MQ-5 / MQ-9 sensors: Detect LPG, methane, CO — cost $3–$10 each.
• For more accuracy, NDIR CO₂ sensors like MH-Z19 are around $20–$40.
• 
  
• Pros: Good for detecting gas leaks or if gas is on but unlit.
• Cons: Doesn’t detect flame itself; more for leak detection.

💡 Use case: Alert if gas is leaking or burner is left on but not burning.

🧠 4. 

Combine Them for Better Results

If you want a reliable system, combine:

• Flame sensor (detects active fire)
• Gas sensor (detects leaks)
• Temperature sensor (detects prolonged heat)

You could connect these to a simple microcontroller (like Arduino or ESP32) and:

• Trigger an alarm (buzzer or light)
• Send alerts via Wi-Fi (if using ESP32 with home automation)

💰 Cost Comparison

Type	Typical Cost	Function
Flame sensor (IR/UV)	$2–$15	Detects visible flame
Gas sensor (MQ series)	$3–$10	Detects gas or CO
Temp sensor (DS18B20/MLX90614)	$2–$20	Detects heat
Thermal camera	$200+	Detects temperature patterns visually