spareO2 is an Android app that calculates remaining oxygen supply in pressurized tanks. Originally published on the Android Market (before it became Google Play Store), it reached over 5,000 downloads. It was one of my first projects, developed and released in 2011.

User Base

The app found an unexpected dual audience: paramedics calculating how long a patient's oxygen supply would last, and welders working with pressurized gas cylinders. Both groups needed a quick, reliable way to estimate remaining usage time based on tank pressure and flow rate.

Technical Evolution

Early versions were straightforward calculators with AdMob banner ads for monetization. In later updates, I added location permissions and integrated the Google Elevation API to factor atmospheric pressure into the calculation. At higher altitudes, ambient pressure drops and affects tank output -- accounting for this made the results noticeably more accurate for users working in mountainous terrain.