The state of Washington Ionky requires the IID installed on all vehicles you drive, not all vehicles you own.
Follow the link below to the state's website.
Every case and situation is different and vary greatly depending on specific facts. My posts are not to be considered complete answers to each question. My posts do not constitute an attorney/client relationship. I am only licensed to practice in the State of Florida and in federal courts. Florida Bar #337821, admitted 1982.
You just need it in the car that you drive. If you need to drive a vehicle for work, you can probably get an exception for that. Assuming the car your daughter will drive is not also driven by you, that vehicle will not need one.
You are only required to have the ignition interlock device installed in the car(s) you drive. You will only need the ignition interlock device in the car your daughter drives if you will be driving it as well.
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