Set your sensors with the top up!
You don't want false alarms when it's raining.
also the steel bars in the top will affect the outer perimeter, but you will want to have it work well in both situations, so check it both ways.
When you are leaving your car unattended for long periods of time, you'll want to put the top up anyways....so what if the alarm goes off when they steal your deck, if you're not there to protect it.

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Charlie Lamble
Sault Ste Marie ON

I'm sure you think you understood what you heard me say, but I hope you realize that what I said is not what I meant