Over on Hackaday we've seen a post about Scott M. Baker's 3D printer filament drying farm that is monitored by a 433 MHz ISM band sensor and an RTL-SDR running rtl_433. If you're familiar with 3D printing then you'll know that it is critical to keep the plastic filament free from absorbing moisture, otherwise it can cause all sorts of issues when it comes time to print something.
To keep them away from humid air Scott uses "PrintDry" plastic vacuum canisters. Unfortunately he found that the vacuum sealing system wasn't perfect, and that some canisters would lose their vacuum after a few days. In order to ensure that the canisters were properly sealed he decided to add some active monitoring with pressure and humidity sensors and a wireless transmitter.
His monitoring system consists of a cheap 315 MHz ISM band transmitter, ATTINY85 microcontroller and pressure + humidity sensor. To receive and monitor the data he uses an RTL-SDR that runs the rtl_433 software, which is a program that is capable of decoding many different types of wireless ISM band sensors.