Silverhand's note is a paper note in Fallout 4.
Location
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It can be found on the body of Luke Silverhand in the church of Jamaica Plain.
Transcript
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Manifest said it was a Type-V Laser Defense Grid. Practically military grade. Whatever's down there, the security's the real deal.
Should be easy enough to let the others in, then reactivate the system. Let the turrets deal with them. No need to get my hands dirty.