The planter primarily senses smell, entry/exit and water level. There is also a mechanical system (construction is going on) that mixes an "appropriate" amount

The planter primarily senses smell, entry/exit and water level. There is also a mechanical system (construction is going on) that mixes an "appropriate" amount of water with pee, so that it is usable by the plant. So in all we can sense: - number of people that went into the planter (approx) - amount of pee was collected - smell levels based on usage/pee levels there are also some more things related to plant growth.