Firstly, find out if you are at particular risk of flooding by looking at the interactive map on the Environment Agency website. www.environment-agency.gov.uk If you are at risk, you can sign up for a free Environment Agency Flood Warning, either online or by calling 0845 988 1188.
Although this interactive map is useful, it does not cover the risk of flooding from surface water or flash flooding, an incident that can happen anywhere after a particularly heavy downpour.
If you are not eligible for a free warning from the Environment Agency, you may like to buy your own flood alarm. There are many different kinds on the market, with varying degrees of sophistication. You can find recommendations for reliable flood alarms at www.environment-agency.gov.uk.