Minimalist and small but precise altimeter based on wonderfull TINYSCREEN+ (PROCESSOR, color OLED, RTC, USB, LIPO battery...) , BMP280 barometric pressure sensor board, and optional micro-sd card to record values.

2 sizes depending if you use micro SD card shield or not.

https://tinycircuits.com/collections/processors/products/tinyscreenplus
https://tinycircuits.com/collections/sensors/products/barometric-pressure-tinyshield
https://tinycircuits.com/collections/all/products/microsd-tinyshield

Example source code here :
https://github.com/pnomblot/TinyCircuit-Altimeter

You can

• adjust altitude référence
• adjust sample interval (1s to 3600s)
• adjust RTC clock time
• display internal temperature
• display battery voltage

Enough precise to detect you go upstairs...