Answer
Should I install smart locks or PIN modules to add mobile keys?
For independent hotels with existing electronic locks, PIN-module retrofits via OpenKey or vendor PIN modules typically beat full smart-lock replacement on cost (USD 3-8 per room per month subscription vs USD 250-600 per door capex plus subscription). For properties with mechanical-only locks or new builds, smart-lock replacement is the better long-term path.
The cost math
Smart-lock replacement: USD 250-600 per door hardware ([Salto](/smart-locks/salto/), [Assa Abloy](/smart-locks/assa-abloy-hospitality/), [Onity](/smart-locks/onity/), [dormakaba](/smart-locks/dormakaba/)) plus ongoing subscription for mobile-key issuance. PIN-module retrofit: zero hardware capex; subscription only (OpenKey at USD 3-8/room/month). For a 40-room property, retrofit pays back capex within 1-3 years vs smart-lock replacement.
When retrofit wins
Retrofit wins when (1) existing locks are electronic and PIN-capable, (2) capital budget is constrained, (3) the property is testing mobile-key adoption before committing to full replacement, (4) the property is in a market where lock-replacement permits add operational delay.
When replacement wins
Replacement wins when (1) mechanical-only locks need replacement anyway, (2) new build with no existing infrastructure, (3) the property wants the deepest PMS integration (Salto KS native cloud platform), (4) hospitality-grade durability is operationally critical (full-service properties with high turnover).