If you tell screeners, they can wand you or possibly do a pat-down. You should have received a wallet-sized card when pacemaker was implanted. Bring card when you visit. PS..not all of the 19 Smithsonian museums have metal detectors. I'm almost positive The Castle doesn't have them.
Speak with the security personnel on scene, they will most likely request to do a hand wanding and check your jacket and bags.
The national gallery of art and the national portrait gallery does not
The castle does not have metal detector however ALL federal buildings including ALL Smithsonian buildings have high security measures.
I am pretty sure the castle doesn't have them , but most of the museums have so bring the card and show it to the security personnel
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