When you check your condition before driving with a personal breath tester, the screen sometimes shows no number, or shows a breath-related prompt or an unfamiliar symbol. The same goes for when the power is off or the app has no record. If you write 0 in the result field out of habit at these times, a test result showing that there actually was no alcohol gets mixed up with a situation in which the test could not be completed.
Zero means something only when it is a value the device presented as a numerical result. A test failure indication, by contrast, means no number was obtained. Personal testing is reference information to help with driving decisions, so on days when you could not complete a result, it is safer to rethink your travel plans than to interpret it as a "low value." Related documents from the International Organization of Legal Metrology (OIML) also distinguish quantitative results from preliminary screening results, which is why the habit of reading carefully what the screen actually shows matters.
The number zero and no result are different records
If the screen shows 0, or a value and unit equivalent to 0, that is one test result presented by the device. Recording the date, time, and unit with it lets you tell later when that value is from. However, this number alone does not settle whether you can drive.
Conversely, a message that the breath was not fully recognized, a power cut during the test, or a symbol whose meaning you don't know is not a result value. Even if it is inconvenient, record the fact that there was no number as it is. The moment you change "no test" into "0," you create a false record that looks like a completed test.
Write down what you saw on screen separately from your interpretation
Rather than relying on memory and concluding "I think it was a breath error," it is better to write down the message or symbol on the screen as closely as possible. The exact meaning of the symbol and the next steps must be confirmed in the actual manual for that model. If you borrow error names from another product's manual to interpret it, your reading may differ from what actually happened.
| What you saw on the screen or app | What to record | What the record does not mean |
|---|---|---|
| A breath-related prompt appeared | The screen message and whether the test was incomplete | A result showing an alcohol value of zero |
| The power went off during the test | When it went off and any battery message on screen | A judgment that the test result is fine |
| Today's value is not visible in the app | The app did not show a current record | Confirmation that no test was done on the device |
| A value from an earlier date is shown | The date displayed, recorded separately from today's date | An interpretation that the past value is the current result |
The app screen in particular may show current readings, past records, and a no-record state differently. That is why the observation that the app has no value is not enough to settle the device's test status. If you write down separately what you checked on the device screen and in the app, you can describe the situation more accurately later when you consult the manual or get support.
Conditions to check before testing again
Repeatedly trying until a low number appears when a test did not complete does not fit the purpose of a self-check. It is better to first check the testing method and retest conditions given in that device's manual. You cannot apply general tips such as "blow harder" or "blow longer" to solve it.
For example, suppose that on the morning after a company dinner, a driver saw a breath-related prompt on the device twice before going to work. The fact to observe is that "neither attempt reached the numerical result screen." Rather than interpreting this as "0 came up twice," if the test still cannot be completed after rechecking the procedure in the manual, it can be treated as not having obtained a result to use for that day's driving decision. In this case, a possible action is to arrange alternative transport, such as public transit, a taxi, a designated driver service, or riding with someone, and the completion criterion is not getting a low number but completing a test normally according to the manual so that you can confirm the number and the completion status separately.
If it is hard to keep blowing or you struggle to finish the procedure after several attempts, there is no need to conclude on your own that the cause is a health problem or a device fault. Just record the actual screen message and when it happened, and check the model-specific guidance. Separating solving the testing problem from deciding how to get around that day keeps you from delaying the driving decision while checking the device.
On days the test is incomplete, change your travel plan first
If the self-check result is incomplete, you do not have a valid personal result for judging whether to drive. Especially if you drank the day before or are worried about your condition the next day, the right conservative choice is not to take the blank result as reassurance but to arrange alternative transport first. Personal readings are reference values and do not replace enforcement test results or legal judgments.
So that you are not making rushed decisions only on days with appointments, you can plan both the ride home and the next day's commute on days when a company dinner or gathering is scheduled. It is also good to agree with your family to say "it showed 0" and "I couldn't complete the test" differently. The latter wording makes clear what help is needed. For example, saying "I couldn't complete the result, so I'll find another way to get there today" lets you adjust your actual travel instead of guessing what the screen means.
Record the reason for an incomplete test instead of leaving a blank
If you leave the result field blank in a paper note or app record, it later becomes hard to know whether it was a day you didn't test or a day you tried but couldn't finish. A useful approach is to separate "not tested" from "test incomplete," and for the latter, briefly record the actions you actually confirmed, such as the screen message, whether you checked the app, and whether you used alternative transport.
The purpose of this record is not to collect many numbers. It is to look back at which days the test did not finish and what you chose instead of driving at those times. Only by recording 0 as 0 when a result was displayed and recording a failure indication as a failure does the record help with your judgment before the next drive.
Note: Self-check results from DATECH products are provided as reference information only. Actual enforcement standards and testing methods may differ by agency and device, so self-check results may differ from enforcement results, and DATECH accepts no responsibility for enforcement results.
