What is the Pen Test (or HGN)?
The Horizontal Gaze Nystagmus (HGN) test, or what is commonly referred to as the “Pen Test”, is a measurement of the extent to which your eyes twitch involuntarily as they move back and forth across your field of vision. The effects of alcohol can cause this. This involuntary twitching is called ‘Nystagmus’. Police commonly use this test on the roadside to help them determine whether a suspect has an illegal blood alcohol content. It is usually the first field sobriety test that police utilize because it is statistically the most accurate if it is administered by police correctly. I know this because I am trained and certified in field sobriety testing – the same certifications held by police.
Difference Between Pen Test and Other Sobriety Tests
Other field sobriety tests, like the ‘one leg stand’ and ‘walk and turn’, measure a subject’s balance, coordination, and ability to follow directions. And thus if a subject has particularly good balance or is more athletic than most, they would tend to fare better on those coordination-related tests. The pen test is different. It is different because no mater how athletic or coordinated you are, you cannot control the twitching of your eyes when you are impaired by alcohol. And so the pen test will usually give you away if you are impaired.
Should You Take the Pen Test?
Your response to reading this will likely be, “hmmm, if pulled over, I better not do the pen test then.” Not so fast. The pen test comes from the National Highway Traffic and Safety Administration (NHTSA) Manual, and the scientists that created this test are united on the front that, in order for the results to be accurate, it has to be administered upon you correctly, or what in Ohio lawyers refer to as ‘substantial compliance’ with the Manual. If the pen test is not administered upon you correctly (enough) then it is not admissible at trial against you. What’s more, if the pen test is not administered upon you correctly (enough) it cannot be used by police to accumulate probable cause for your arrest – which will often cause any breath test that you gave (or refusal thereof) to be deemed inadmissible against you at trial. That’s a big deal.
How Good are the Police at Administering Correctly?
So, given this dynamic, how good are police at administering the pen test correctly? Simple answer: not very good. I have seen only one Officer (out of hundreds) over my career administer the pen test perfectly. And less than half of the officers that I observe administering the pen test (whether on video or in court) are doing so correctly enough for the results to be admissible at trial. Further, even if the Officer administers the test correctly enough for it to be admissible in a trial against you, it is overwhelmingly likely that the officer will not strictly comply with the NHTSA Manual, and so your attorney can still effectively challenge the weight of the pen test at trial. So why don’t police just learn the pen test correctly and administer it correctly to everyone? Good question.
If You Refuse the Pen Test…
On the other hand, if you refuse the pen test on the roadside, police and prosecutors can tell the jury that you refused the test – that never looks good for obvious reasons. If you get stopped, you may be better off submitting to the pen test. The chances of it negatively affecting your case are slim, but to refuse the test implies guilt. (NOTE: the analysis is different for a breath test, so see my blog posts concerning breath tests for information on that subject).
Other DUI/OVI defense lawyers in Ohio may advise you to refuse the pen test. If you ever hear this from one, ask that attorney whether he/she is certified in field sobriety testing. I’m guessing the answer will be ‘no.’
 Between 77% and 88%. (2013 NHTSA Manual, Session 8, pp. 5-10).