Small, cheap, low-powered sensors are still a challenge to make. LoRa-Tooth uses $6 BLE modules to make untethered sensors with long range.

Today, we have a lot of tools for building wireless devices. The ESP8266 is probably on the top of the popularity list. It ticks off a few important requirements

Accessible: really cheap, lots of people can afford the $4 ESP8266 on ebay
Community: large ecosystem of sensors and peripheral support because of Arduino
Integration: easy to integrate into other platforms using protocols like MQTT
Low Complexity: Easy to use IDE, not much tool chain setup
Hardware exists, and in useful form factors (easy to build with, as long as it’s wall-powered)
All of these factor contribute to maximizing “makability”. The ESP8266 and other WiFi microcontroller boards make it easy to build IoT devices when size and power consumption isn’t a factor.

But in 2018, it’s still a big challenge to build practical battery powered sensors. It’s still hard to make a DIY open/close sensor for a door or window - one that’s small, not ugly, will last for a couple of years on a coin cell battery, and can be built for less than $10. There doesn’t exist a platform that checks off the same makability features as the ESP8266 for battery powered projects.

I’ve seen herculean efforts to make the ESP8266 battery powered, but those approaches typically sacrifice too much (physically too big, still not energy efficient enough, or lose the ease of programming and peripheral support because of switch to IDF and proprietary radio protocol). Other wireless sensor projects use 433MHz or 915MHz transceivers and an ATtiny, but still end up kind of big and not low power enough for what I need.

The popularity of the Amazon Button is evidence of these challenges. It’s still hard today to DIY a simple, portable, battery powered IoT button that won’t cost more than the $5 Amazon Button. The popularity of the Amazon Button hack, given its very limited functionality, is an indication that we need better platforms for low powered IoT devices.

Enter the Nordic nRF51822

Let me tell you about this BLE modules that’s been flying under the radar of the maker community. It’s the nRF51822 from Nordic Semiconductor. For reasons I don’t understand, this Nordic BLE module is available from quite a few sellers on eBay and Aliexpress. And it comes in a few useful form factors that make it easy to build with. And it’s pretty cheap.”