Portable weight sensor

I am planing for do a project that measure the amount of pills in a portable container ( fit into pocket ). That container consist of weight sensor, planning to integrate with Arduino, so that it can notify the mobile app when the volume of pills drops below a predefined threshold.

Any suggestions/recommendations hardware to use ?

Thanks in advance

Weight depends on gravity. This means the container needs to be vertically above the sensor and free of anything touching it. It also needs to be stationary for accurate reading.

These would appear to make it difficult to use when in a pocket.