A Honolulu startup is putting cheap, fast-to-install water sensors across Hawaii, which is good news for emergency crews and people living near flood-prone streams and roads.

• The US has almost no flood monitoring — under 300 tide gauges for 95,000 miles of coastline, and even fewer sensors inland.
• Honu, based at the Manoa Innovation Center, builds small sensors that are cheaper and far quicker to install than the government's gear.
• During Hurricane Kiko, the state's official gauge at Wahiawa Reservoir went dark while the local sensor kept reporting.
• The sensors track stream and coastal water levels every second and send the data over cell networks, including on roads that normally stay dry.
• Warmer air is driving more frequent and more intense flooding, both on the coast and inland.

Outlook: Sensors go in at seven more reservoirs around the state within weeks, with the company aiming to sell the same setup to cities and states on the mainland.