As the mercury rises, the heatAlert service sends out warnings by text, voicemail or email when a heatwave or very hot weather is forecast.
The service, which runs until September, is particularly aimed at people with respiratory or cardiovascular conditions, vulnerable residents, parents of young children, carers and healthcare professionals.
It is managed by the Sussex Air Quality Partnership, which also sends out airAlerts warnings when moderate or high air pollution levels are forecast and coldAlerts during winter months when extreme cold weather is forecast.
The partnership is hosted by East Sussex County Council and includes representatives from all local councils in Sussex.
Cllr Nick Bennett, East Sussex County Council lead member for transport and environment, said: “Many of us look forward to warmer weather but for some, rising temperatures can be a cause for concern.
“The free service will give people such as those with long-term health conditions and older people advance notice when very hot weather is on its way to their area.
“This way, people can make preparations such as ensuring they have water, medication and other essentials with them, covering up in the sun or staying indoors if necessary.”
Subscribers to the scheme will be sent alerts about when, where and for how long a severe hot weather event is forecast via text message, voicemail or email.
People can sign up to the scheme by registering online at www.heatalert.org.uk, emailing email@example.com or calling 01273 484337.
The service also has a presence on Twitter @heatalertsussex