The talk demonstrates a working system made of an Elixir program running on a Raspberry Pi that scans the Wi-Fi spectrum and collects presence data; an AWS Lambda JavaScript function that receives those data and stores them into a DynamoDB instance; a Telegram bot, also running on Lambda, which sends alerts based on the number of presences. The focus will be on the overall architecture and the most important parts of the code. We'll show some Lambda automation tools and how to test the components locally. All the source code will be on GitHub. Ideal talk to get started with those technologies.