On the Pilots you access it by removing the glove box.

Not that you asked but here's my 2 cents on what you're thinking about doing.

The new unit is going to have to be programmed. And if there's a problem doing that the mechanic is going to (rightly) say, that's your problem because it's your part.

Who knows, maybe it was dropped at some point during shipping and got damaged. Maybe it's just a factory defect in that particular unit.

If he provided it it's not your problem, it's his. He'll just return it to his supplier and get another one and program it and you won't even be bothered about it.

Or, what if it fails in 6 months? Again, he'll (rightly) say, Hey, you provided the part, take it up with your guy.

If he provided the part he has to replace it and program the replacement unit.

So there's a lot of risk with providing the part yourself and you should weigh how much money you'll be saving compared to the potential headaches you may be facing if things go wrong

addendum

On some of those Hondas and depending on what exactly fried in the Smart Power Unit you could stop the symptoms by unplugging the hood latch sensor wiring connector (on the hood latch).

So if the alarm is going off randomly or it's making weird clicking noises or messing with the dash lights, sometimes by unplugging the hood latch sensor you can prevent the system from doing that.

The car thinks the hood is open so it won't arm (or try to arm) the system.

The downside is that the alarm won't be armed after you lock your doors and you'll get the little warning light on the dash saying hood ajar.

Posted by: @fadyrofa

I found it cheap online

beware of cheap online electronics. You usually get what you pay for and end up doing the job again.