"At at DUI roadbloc?"
No it does not. A Breathalizer is only able to detect alcohol that you exhale into the machine. It is not able to detect cannabis. A blood test and a urine test can detect cannabis. the urine test does not test for THC (the active ingredient that causes you to get euphoric) it only tests for the non-psychoactive cannabis metabolite.
For a single use of cannabis it (non-psychoactive part) can be detected in the urine for between about 1-7+ days and for a regular user between 7-100 days. A blood test can detect cannabis for approximately 12-24 hours and in a regular user between 2-7 days.
Perry Solomon, MD