Design considerations

A project log for 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

arikArik 04/25/2017 at 07:320 Comments

There are existing solutions out there to prevent such tragic incidents. Starting from printed stickers and up to complex IoT systems connected to the cellular network. I am not inventing something new. So what made me design and implement a system of my own? The reason is that I was not happy with the existing systems for various reasons. I will describe my key requirements for such a system in more detail.

But first a short disclaimer: any device you might use for this purpose is a backup. It is not meant to be a replacement for your responsibilities. It is merely a last resort when all else has failed. Having said that, I think that installing a device like this is a responsible thing to do, because even though the chances are slim, cases like this happen yearly.

Alert, not a reminder

It is all about the timing and the level of certainty of the alarm. Many systems will notify you that a child seat is occupied when you open the door, turn off the car or stand up from the driver’s seat. However, that is merely a reminder. You might have just been planning to open the back door and take the child with you, but the system doesn’t differentiate. Worse, you might hear the reminder and plan to take the child, but then something might happen and you might get distracted. When using a reminder system, you would get these reminders all the time, as often as several times a day. You might get used to these reminders, they might lose efficiency and affect your routine.

A key requirement for Fochica was to be an alert. Meaning to know when the adult left without taking the child out of the seat and to sound an alarm at that time. This should be a rare event, probably due to a false positive rather than an actual incident (which are very rare). Such an alert would draw much more attention due to the context and certainty it conveys.

To know when the adult and the car are apart, some type of communication must happen between the two parties. Additionally, each of the two parties must have a device to facilitate the communication, a receiver and a transmitter. Naturally this makes an “alarm” system more complex than a “reminder” system but since an alarm can also fall back to being a reminder, I couldn’t see any other cons for this design.

No dongles

Some similar implementations are available where an adult must carry a special dongle/keyfob that communicates with the device in the car. A key requirement for Fochica was to use something that a user would already have, a smartphone, as the “terminal” for the adult. This way I didn’t have to design a compact device for the adult, overcome challenges of reliably powering it, increase the cost by introducing more parts, etc. Using the phone also carries several advantages, such as a rich UI, IoT connectivity, etc.

The decision to use smartphones for one side of the communication basically limits the communication protocol options to Wifi, Bluetooth and BLE. I have decided to use BLE due to the low energy property and the growing support in smartphones. BLE modules are also available for as low as $3 on eBay so they are “approachable” for hobbyists.

The downside of this approach is the dependency on the smartphone. The assumption is that we now carry our smartphone everywhere with us. The chance of having the phone with us is high and the chance of forgetting both the phone and the child in the car is lower than forgetting just one. Still, if the phone is not available, the device in the car will operate in “reminder” mode as a fallback measure.

Low overhead

Some implementations exist where the user must turn the system on when placing a child in the seat (arm it) or turn it off when taking the child out, or put a beacon on the child, or start an app, or do something on a routine basis that he wouldn’t have to do if he was not using such a system. This creates nuisance to the user and faced with the low chance of an incident like this happening and the belief that “it won’t happen to me” many parents decide to not install or abandon the use of such a system.

Remember, there is not legislation on this matter for private cars, so the willingness of users to install a system like that depends largely on the balance between being proactive and the amount of effort the device will require from the user.

Due to these considerations, it was important that Fochica works automatically once installed. Not requiring any action that you wouldn’t otherwise do normally. This means the system must detect if the seat is occupied and when the adult is in range without any human input. I find the overhead of installation of lesser importance. Systems that are easy to install but hard to operate day to day seem to miss the point in my opinion. The difficulty of installation should be reasonable and most importantly shouldn’t mess up other systems in the car or seat.

To prevent a scenario of a “silent failure”, where the device is not operating correctly without the user being aware of it, Fochica provides audible feedback when the state of the seat changes, additionally a visual feedback (LED) can be added to represent connectivity state, seat state or both.


Another requirement of this project was that it would be low-cost. For it to ever reach wide use and remove any financial barriers the device has to be cheap. The key components: Arduino, BLE module, step-down converter can all be purchased together for under $10 on eBay. The parts that were used in the design are all available in single item quantities to allow for hobbyists to obtain them. The choice of the popular and widely available Arduino platform is also a result of the same requirement.

Comparable commercial systems cost around $200-300 and require subscription fees or cellular fees which add a recurring cost. It is understandable that making a commercial system carries additional costs such as manufacturing, stock, distribution, support, etc. Still savings of $300 plus over 3 years of use is a significant value and can encourage wider adoption of such systems, something that hasn’t happened yet.

Support for several adults, cars

Supporting several seats is trivial, but many available implementations fail to address scenarios with two adults or two cars. Imagine a family where both parents use the car. One day the two parents and their child stop near the grocery store and the driver goes to get some groceries. The other adult and the child stay in the car. Should an alarm sound?

To address these scenarios, the device should be aware of any number of registered adults and should differentiate between any adult leaving the premises and the last adult leaving the premises. This is also one reason why a design with a simple BLE beacon in the seat is much less useful than a complete Fochica system.


As you can see there were plenty of considerations. It was important to shift the complexity from the hardware to the software because the software can be duplicated easily whether one still needs to build each Fochica device independently. More work must be done to simplify the build so it is easier for the end user to assemble. I encourage you to build a Fochica and send your feedback. If you have good ideas on how to simplify the build or take it to the next level, please let me know.