Audible/Vibratory liquid level indicator
Ideal for making a cup of tea or coffee with milk. Place the device on the side of a cup and it will let you know when the liquid has reached the top through a series of audible beeps or vibrations. Can also be used as a single level sensor such as for non-mixed drinks. Handy magnets on the back of the unit allow for easy storage on the fridge or other metal objects.
You can hear what the liquid level indicator sounds like below.