Introduction: Fochica - Forgotten Child in Car Alert

Fochica, forgotten child in car alert, is a no hassle, low cost and extensible system that helps prevent forgetting children in vehicles.

Kids who are left alone in cars are likely to suffer a heat stroke with dire consequences. If you have never heard about this phenomenon before, your first reaction is probably "who forgets their kids in a car?" or "that would never happen to me!". That is a natural psychological response but in reality, cases like this happen over and over again every year. Why not use technology to make sure you don’t forget your kids? Fochica’s mission is to prevent forgetting children in vehicles and thus save children’s lives.

Fochica™ is comprised of a Fochica open hardware, open software, Arduino-based device that is installed in a car and a Fochica app that is installed on the driver’s smartphone. Sensors monitor whether the child car seats are occupied or empty and send the data to the device. The device communicates with the app via BLE passing the information to the driver. When the driver’s smartphone goes out of range and a seat is occupied an alarm will sound on the smartphone.

Fochica is an alert, not a reminder. Meaning it will not nag you to “not-forget” your kid when you turn off the car or when you exit the vehicle. It is designed to alert when you have forgotten, which Fochica considers as being out of BLE range while a seat is occupied.

Step 1: Materials and Tools


  • Computer for programming the Arduino
  • Android smartphone with Bluetooth Low Energy (BLE) for interfacing with the device
  • Soldering iron [optional]


  • Arduino Uno - also tested with a Mega
  • HM-10 BLE module (or compatible clone) - must have a STATE pin - tested with HM-10, CC41A, MLT-BT05
  • Logic Level Converter [optional] - if your module has 3.3V data lines
  • Passive buzzer - preferably on a module with a transistor
  • NPN transistor [optional] - if your buzzer is not on a module
  • 7-25V to 5V step-down buck converter module - preferably one that is efficient at low currents
  • Magnetic (reed) switch [optional] - set of reed and magnet, such as ones used for doors or windows
  • Breadboard / perfboard / protoboard


  • Wires
  • Various resistors
  • Connectors, plugs
  • Aluminum foil - for the capacitive sensor

Step 2: Connecting the Parts

Connect the parts per the diagram.

In the car, the Arduino should be powered by a step-down buck converter that outputs 5V. You can plug it in to the USB port or, if that is not available on your converter, directly to the 5v and Gnd pins. The USB port is preferred as it provides some additional protection. When working on the circuit in the lab it is fine to power the Arduino through the usual USB connection. See this article for guideline on choosing a dc-dc conversion module.

Check if your BLE module requires 3.3V logic or 5V logic. If you are not sure, look in the specs or on the PCB of the module. If 3.3V logic is required, use a logic conversion chip/module or you can make a voltage divider with two resistors to drop voltage on Arduino’s Tx pin by 2/3. See this article for comparison of the different BLE modules.

Fold a piece of aluminum foil to a size that will fit comfortably under the padding of the seat and secure it to a wire (i.e. with a paper clip). That will function as a capacitive sensor.

Step 3: Arduino Code and BLE Configuration

BLE module configuration

Once you correctly connect the BLE module to your Arduino, try to upload and run the Arduino BLE Ident-n-set sketch to identify and configure your BLE module. This will also help you confirm that your BLE module is working as expected. It is recommended to change the default module name to something unique. You can do that with the sketch or manually.

Use nRF connect on your Android phone to connect to the BLE module and send/receive packets.

Some modules need extra configuration if they output a "blinking" signal on the STATE pin. The sketch can help you with that. Also feel free to ask questions in the comments section below.

Device code
The Fochica Arduino code is available at GitHub. You can customize the various modules, add or remove sensors, etc. At first I recommend to stick to the default configuration. At least until you feel comfortable with the design.

Step 4: Android App

The Fochica Android App is available at the Google Play store for free.

Once you install the app, add your BLE module in the "settings" screen. It helps if you module has a unique name.

Please understand that the project is in prototype stage. The app was not tested with all smartphones. Your feedback is very welcome.

Step 5: Connecting the Device in the Car


The device should be connected to a source of constant 12V power coming from the car's battery.

The connection points are at the input terminals of the step-down converter and at the 12V plug terminal in the schematics. The 12V plug is used by the Arduino to sample the charge level of the car's battery and is using a voltage divider to drop the level to Arduino acceptable range. Do not connect the Arduino directly to 12V.

Possible sources of 12V in the car:

  • A "cigar" socket
  • An OBD2 socket
  • Tapping from a fuse box
  • Directly to a battery

If your cigar socket doesn't provide power when the car key is out of ignition mode it might be possible to rewire the socket to supply constant power. A "fuse tap" can be used for this purpose. Please provide information about your situation in the comments below and I will try to help.

Make sure there is a fuse on the line you are using. Especially if you are tapping wires directly vs using existing connectors. They fuse should be low. 1A or 3A is preferred.

Integration with the Seat

Place the device next to the seat and secure it such that it doesn't move around while driving.

Place the "capacitive sensing plate" (aluminum foil) under the padding of the seat. Adjust exact position later for best sensing.

Secure the reed sensor and the accompanying magnet part on a belt buckle such that the circuit is closed when the buckle is locked and open when the buckle is open. Sticky tape works well for this purpose.

Step 6: Summary

I hope you like the project and think that our mission is worth of your support.

The end goal is to create a consumer device that everybody can use. Where the device is low cost and all the details are an open specification.

Vote for Fochica in the "Instructables 2017 Microcontroller contest", like and follow this instructable.

More information is available on the Fochica site and Hackaday project page.

Licenses and legal: Project disclaimer, Arduino code is GPL, App has a EULA.

The project is in prototype state and any feedback from the community would help it a lot. If you have any questions or if you want to build your own Fochica, please get in touch.

Microcontroller Contest 2017

Participated in the
Microcontroller Contest 2017