Three bikes have been stolen in the last 24 hours in the city. Addresses affected were in Hurstwood Road, Hadleigh Road and Fordfield Road.
Inquiries are on-going into the bikes thefts and police are appealing for witnesses.
Local Neighbourhood Sergeant Ash Hopper said: "Thieves are jumping into gardens to steal bikes that have been left lying on the ground or against a wall and not chained to anything.
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"People might think if the bike is in their garden it is safe, but if it is left lying on the ground and it is easy to access the garden it is at as much risk of being stolen than if it is left in the street.
"We want to make sure our communities are protected as much as possible from thieves and are doing everything we can to target known criminals and catch those responsible but despite our best efforts there are still opportunist thieves who take a chance.
"It is really important that local residents work with us and make their property is as secure as as it can be to deter these opportunitists."
Following the thefts, police are issuing storage advice to the public, and reminding them to make sure their bikes are secure.
Bikes should be kept in a secure shed or outbuilding, if possible, or alternatively inside your home.
Sheds and outbuildings should also be secure with good quality locks and ideally bikes should be chained to a secure post inside.