A police operation to covertly follow a man came to an abrupt halt when the man found tracking devices planted in his car, ripped them out, and listed them for sale on Trade Me.

Ralph Williams, of Cromwell, said he found the devices last week in his daughter's car, which he uses, and in his flatmate's car, when the cars were returned by police after being seized and searched.

Police have neither confirmed nor denied they placed the devices. But Mr Williams said a mobile phone Sim card in one of the devices appeared to transmit messages to the mobile phone of Detective Sergeant Derek Shaw, of Central Otago CIB.

Mr Williams also claimed he had e-mails from Mr Shaw saying: "If you have got something of ours it would be good to get it back. You can call me and I can come meet you."

Mr Williams placed one of the devices on Trade Me with a price of $250. The ad read: "Used government covert surveillance tracking. No police to bid on this ..."

A Trade Me spokesman said the listing was removed yesterday "at the request of the New Zealand Police".

Mr Williams said the cars were seized after an unmarked police car was torched in Alexandra in July. An investigation found nothing on him.

Mr Shaw would only say yesterday: "Police use a variety of legitimate investigation techniques. However, it is not the policy of the police to comment on those techniques or other operational matters."

The Summary Proceedings Act says a warrant should be obtained for a tracking device but one can be installed without a warrant if there is not time and an officer believes a judge would issue one if time permitted.

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