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Cheap and fast: Aluminum foil and tape are household staples — no special equipment required. 
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Visible tamper indicator: It provides a quick visual cue: intact = probably undisturbed; torn or missing = possible entry or attempt. 
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Good for short absences: Handy for short trips, deliveries, or when you want peace of mind during a nap or quick outing. 
⚠️ Important Limitations (Don’t Treat It as a Security System)
This is a simple indicator, not a prevention method. Here’s what it doesn’t do:
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It won’t stop an intruder. Anyone who knows the trick can remove the foil and tape carefully, or bypass the knob entirely (e.g., through a window). 
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It can give false positives. Wind, pets, kids, a careless roommate, or a delivery person could disturb the foil. 
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It doesn’t record when or who — you only get a yes/no-ish signal that something was touched. 
 
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It can be checked or replaced by a clever intruder before you get home. 
Because of those limits, don’t rely on foil as your only security measure — think of it as a low-cost supplement.
👍 When This Trick Actually Helps
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You want a very quick visual indicator for short absences (grocery runs, quick errands). 
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You’re in a shared home and want to know if someone (roommate, housekeeper, maintenance worker) used the door while you were out. 
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You need a no-tech solution (e.g., temporary renters, short vacation) and don’t have a smart lock or camera. 
🔐 Better (and Complementary) Security Measures
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