As you likely know, you can get a DWI charge if you are arrested with a blood alcohol concentration (BAC) of 0.08% or higher. You can also get charged if you’re below this level, but other evidence of impairment is needed. With a high enough BAC, it can be assumed.
In some cases, people decide that all they need to do is show that they’re below that line to shake the charges. For instance, you may think that there is no other evidence, so proving that you had a BAC of 0.07% or less will change the court process enough to have those charges dropped.
To this end, you may consider ordering your own “Breathalyzer” device online and using it before you get in the car. If it shows that you’re under the limit, will that get you out of the charges?
Your results are not proof nor useful as evidence in court
In short, no, the results from your own testing device are not proof of anything, legally speaking. It’s impossible for the court to know if your test is accurate. The device is not an approved model, for one thing, and you administered the test yourself. The results are essentially meaningless.
Even the portable breath tests that police officers carry have been criticized for not being accurate or reliable. They’re generally not used in court. They’re just a means to show that you should come to the station for a more comprehensive test, such as a real Breathalyzer or a blood test.
That doesn’t mean there are no ways to fight these charges, of course. Just be sure you know what legal tactics you can actually use.