Lincolnshire's 46 flood warning sirens will be set off on Wednesday morning.
The annual test is to make sure all of the county council sirens are working ahead of the winter.
Sirens will sound along the coast at North Somercotes, Mablethorpe, Boston, Skegness, Spalding and Sutton Bridge, plus inland at Louth, Horncastle, Middle Rasen and Gainsborough.
These are the areas most at risk of being hit by floods. The warnings aim to reduce the impact of heavy rain.
If the sirens are sounded after Wednesday's tests, it means a flood warning is in force and a countywide emergency plan tells the public to listen to BBC Radio Lincolnshire for more information.
The sirens can be sounded en masse or individually after a severe flood warning issued by the Environment Agency, with low-lying Lincolnshire at more risk than other areas.
The 2004 testing of the sirens had to be delayed after heavy rainfall because there were concerns residents who heard them might have thought they were in real danger.