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Will a Smart Lock Fit? Prep, Signal, and Battery Checks

Updated October 11, 2026

Fit is four checks, not one

A retrofit smart lock replaces only the interior escutcheon, so the existing prep must already be right. Score four checks: single-cylinder deadbolt present, wood or fiberglass door, thickness between 1-3/8 and 2 in, and at least 2-1/2 in of interior clearance to the nearest trim. Below 4/4, get a model-specific survey.

Signal decides the protocol

Estimate 2.4 GHz RSSI from router distance plus roughly 9 dB per wall. Above -65 dBm suits direct Wi-Fi. From -65 to -75 dBm, add an access point or switch to a hub protocol. Below -75 dBm, do not buy a Wi-Fi-only lock for that door.

Battery math before the purchase

Wi-Fi drains fastest and Z-Wave or Thread slowest. Freezing weather cuts alkaline capacity first, so cold climates should prefer lithium. Estimate the replacement interval as a range, treat the low end as the shopping trigger, and keep one spare set per lock.

Confirm egress and outages

Double-cylinder conversions must preserve code-compliant egress. Before sign-off, test the lock with dead batteries, dead internet, and the physical key. A lock that fails closed without a key override is a lockout waiting to happen.