Business expense

I don't have a fact answer but to me that's like saying I got a speeding ticket on my way to a lawncare job and it should be a business expense.  Nope.

I once had an electrician trying to deduct lasik eye surgery.  He was told that it wasn't a deductible business expense.  His response was that he should be able to deduct it through his corporation because he needed to see to do his job.  The moral of the story is - you can justify anything if you try hard enough........... but that still doesn't make it deductible.

I think I disagree with the other answers.  I don't see why it can't be a vehicle expense (if they use Actual Expenses).

This isn't a fine or penalty to the government for doing something illegal.  It is a fee to maintain their legality to drive.

Here's the answer.  Tell him to consult with a tax professional

Your tax professional may tell you that when it comes to IIDs, commonly required for individuals with drunk driving convictions, in most cases for 2024 these expenses are not tax-deductible for personal use. The Internal Revenue Service (IRS) generally considers IIDs as personal expenses rather than deductible business expenses.

However, there can be exceptions. Be sure to ask your tax professional if you are an individual who demonstrates a legitimate business reason for requiring an IID, such as for a company vehicle or as part of employment conditions. If so, the expense may qualify as a deductible business expense. It's important to consult with a tax professional to ensure you are complying with IRS guidelines.

https://www.breatheeasyins.com/knowledge-center/are-ignition-interlock-devices-tax-deductible-in-2024