Three-Prong Liquid Level Indicator - Black - Never again risk the embarrassment and inconvenience of overfilling your dinner glass or coffee mug with this alerting liquid indicator. Ideal for those with low vision, this tech-savvy, vision impairment device will offset messy clean ups. Hang this low vision liquid level indicator on any cup or glass with a rim thinner than 3/8 inches and you'll know when to stop pouring. A chirping noise is sounded when the low vision primary sensors are touched by liquid. If the liquid continues to be poured and contacts the secondary sensor, a higher-pitched chirping noise warning you to stop will be sounded.