Sometimes, if you are groggily taking a shower in the morning without paying much attention, you may forget whether or not you’ve already washed your hair (Figure 1).
Fig. 1: DID I WASH MY HAIR ALREADY??????
Fig. 2: The shampoo bottle is no help; it’s probably going to be look the same whether or not it was recently used, unless you do forensic-level analysis of the number of water droplets on it.
You can, of course, always wash your hair again, but then you wasted both time AND shampoo.
What if the bottle itself could indicate (in a simple and electronics-free way) when it was last used?
Here are two possible ways for a shampoo bottle to indicate when it was last used, without requiring any significant user interaction or complex mechanisms (see Figures 3 and 4).
Fig. 3: This bottle has an embossed button-like section that pops out (side view at far left and far right). The default state of the bottle is at left. When you use it, it is natural to hold it in a position that presses in the “button,” resulting in the pressed-in situation (right). Later, the button will pop back out of its own accord.
Fig. 4: Part of the bottle could be made of a plastic that darkens when wet. In this case, the mockup is for a thermometer-sized area of the bottle to be made of this material; the dry material is white (shown in A). When the bottle is turned upside-down, water sweeps along the “thermometer” and darkens it, resulting in the dark gray area in B. Evaporation will eventually dry the “thermometer” and restore its original color.
PROS: Saves time and shampoo.
CONS: May add manufacturing costs and additional product waste.