Floater that closes the electrical circuit to beep out sound when desired liquid level is reached is simple and yet very effective. Simple mechanics and circuitry could result in low-cost solutions so that it may become accessible to most people in need.
Exploring ways to minimize devise contact with liquid.
Make the device less bulky.
Liquid level alert indicators are available in market. They are much compact. Their contact with liquid is quite minimal as such contamination possibility is less and cleaning could be easy. Their cost is rather high.
Students can explore creating solution for multi liquid level indicators by incorporating sensors. For example, multi-level indicator is useful if it can beep once at half level, beep twice at 3/4th level and beep continuously at full level. User will have choice to stop filling at desired level.