Great idea- GREAT product!
Bought it for my recently blind elderly mother who was very frustrated trying to draw a cup of liquid. Che would put one finger in the glass to feel the fluid level. That was ok for cold stuff but hot coffee was a different problem. Sghe always wanted to remain independent and this product helped her achieve that goal and not  be dependent on anyone else! Workd well- two tones: one when nearly full and another when full. Uses standard 9 volt battery plugged into the bottom of the holder and hung over the edge of the glass.  It virtually lasts forever! Great idea- great product!
Rating: 5 stars