If you enjoy hiking or camping, or simply want an easy way to monitor your environment on the go, then the Xpedit by DIYmechanics could be just what you need. It uses a BME280 sensor to detect temperature, humidity, air pressure, and altitude, all of which is fed to an ATmega328P microcontroller that runs the device.
Readings are displayed via a 128×64 pixel OLED screen, and a piezo buzzer and small vibrating motor are used for notifications. Input is provided by a rotary encoder as well as a simple on/off switch, and you can set up warning levels if you want to know if a parameter goes beyond a certain threshold. The device runs on a 1000mAh 3.7V LiPo battery, which enables it to operate for days between charges.
Everything is housed in a nice 3D-printed and spray painted enclosure, and with a fairly compact frame it should easily fit in a backpack or perhaps a rather large pocket for your next trip. It even includes a hole for a lanyard, allowing for neck-mounted monitoring if you so desire, and there’s a tiny compass integrated into the frame to help you find your way back to civilization. Project files are available on GitHub if you’d like to build your own.