Four cars were targeted in Narvick Close, Maldon, within hours of each other.
Nothing was stolen from a silver Kia Sorento but an ipod Nano was taken from an unsecured red Ford Focus and money stolen from a blue BMW 5-Series on June 22.
The key to an unsecured grey Jaguar S-Type was also stolen overnight on the same date.
A silver Ford Mondeo was also entered overnight on June 20 but nothing was taken.
An Essex Police spokesman said: “We advise to ensure that vehicles are left secure and valuable property is not left on view.
“If anyone has any information regarding these crimes please contact Maldon Police.”