Check points are generally established to detect offences pursuant to the Land Transport Act. In particular Drink Driving or Driving Whilst Disqualified.

If you are the driver of a motor vehicle, then you must;

-stop if requested,
-Provide the police officer with your details if requested. (Name, address and date of birth).
-Blow into the device and provide a sample of your breath if requested.

There is no device available in New Zealand to detect driving under the influence of drugs. You may be asked to participate in an impairment test where a trained police officer will ask you to perform different tasks to establish whether you are high/ impaired. If the officer determines that you have failed the test he or she will call a doctor who will then come to take a blood sample from you to determine whether there are any drugs in your system. If you decline a blood test at this stage in proceedings you will be charged with Refusing to provide a sample.

In limited situations the police can search you or your vehicle without warrant.

These situations may include police searching for drugs or stolen property. The police however need reasonable grounds.
Eg. The vehicle may smell of cannabis or the driver looks rather wasted.

Do not consent to any search. Advise the police officer “I do not consent to this search” Ask the police officer “What is your lawful basis for searching me” and ensure that the police officer records it in his notebook. You should not resist the search as this will likely result in charges being laid.

I have also encountered police checking a vehicle to see if it is road worthy, this testing has included checking the spare tyre in the boot and testing the seat belts. These tests of course give the police wide access to the vehicle and could result in items being found that lead to criminal charges.