By Pop-A-Lock of Sarasota-Bradenton and Pop-A-Lock of Venice, North Port, Port Charlotte
December 12, 2025
A master key system is a specially designed locking setup where:
- Every individual door has its own unique key (called a change key) that opens only that door.
- There is one (or more) master key(s) that can open every door in the group (or in the entire building).
- You can also create multiple levels of master keys (sub-masters, grand masters, great-grand masters, etc.) so different people get exactly the access they need — and nothing more.
Think of it like a hotel:
- Your room key opens only your room.
- The housekeeper’s key opens all rooms on the 3rd floor.
- The manager’s key opens every door in the entire hotel.
That is a master key system.
How Does It Work (The Pin Tumbler Example)
99% of master key systems today are built on the common pin-tumbler lock (the same kind you have on your house). Inside each lock there are 5 or 6 stacks of pins (upper pins = driver pins, lower pins = key pins).
Levels in a Master Key System
| Level | What it Opens | Who Usually Carries It | Example Key Marking |
| Change Key (CK) | Only 1 door or 1 office | Regular employee | KA1, KB3, 101 |
| Sub-Master (SM) | All doors in one department, floor, or wing | Department manager, housekeeper | A, B, 3rd Floor |
| Grand Master (GM) | All doors under several sub-masters | Property manager, head of security | GM |
| Great Grand Master (GGM) | Every lock in the entire building or campus | Owner, top-level facilities director | GGM |
Common Real-World Examples
| Business Type | Typical Master Key Structure |
| Small office (15 doors) | 12 individual keys + 3 departmental sub-masters + 1 Grand Master |
| Apartment building | Each tenant = change key → their unit only
Maintenance = master for all units Manager = GGM for every door including laundry, roof, office |
| Large university | Change keys → individual labs/offices
Floor masters → one floor Building masters → one building Campus Great Grand Master |
| Retail chain (20 stores) | Each store has its own master
Regional master opens every store in the region Corporate GGM opens every store nationwide |
Types of Master Key Systems
- Simple Master Key System = One master opens everything, every lock has its own unique change key. This is a 2-Level Master Key System.
- Grand Master Key System = One GM + several sub-masters. This is typically a 3-Level Master Key System.
- Great Grand Master Key System = Used for very large or complex buildings is typically 4 Levels or more.
- Cross-Keyed System – A few selected change keys intentionally open more than one door (e.g., a janitor’s key opens every restroom on multiple floors even though those doors have their own normal change keys).
Advantages
- Huge convenience – the owner or facilities manager carries only 1 or 2 keys instead of 50.
- Tight control – fired employees only have their change key; you rekey only their lock.
- Fast emergency access for security, maintenance, or fire department.
Disadvantages & Security Trade-offs
- Compromise risk: If the master key is ever lost or stolen, the entire building is compromised → you must rekey everything (can cost thousands).
- Slightly lower security: Adding master wafers creates more possible shear lines, so a skilled picker has more opportunities.
- Higher cost: Master-keyed cylinders cost 30–100% more than standard ones, and the initial keying chart/setup labor is significant.
Restricted / High-Security Master Key Systems (Most Businesses Choose These Today)
To solve the “lost master = disaster” problem, almost every commercial master system today uses patented, restricted keyways:
| Brand | Key Control Features |
| Schlage Primus / Everest | Patented side milling + sidebar; keys only duplicated by authorized dealers with signature card |
| Medeco³ / Biaxial / KeyMark | Angled cuts + sidebar; utility-patented until 2021–2027; virtually impossible to duplicate |
| ASSA Twin V-10 | Dual sidebars, extremely pick-resistant |
| Mul-T-Lock MT5+ | Telescoping pins + magnetic pin option |
With these, even if someone finds your master key, they still can’t copy it without proper authorization.
How Much Does a Commercial Master Key System Cost? (2025 ballpark)
| Scope | Approximate Cost (USD) |
| Small office, 10–15 doors, standard cylinders | $1,200 – $2,500 |
| Same job with Schlage Primus or Medeco high-security | $3,000 – $6,000 |
| 50–100 doors, multiple levels + patented keys | $8,000 – $20,000+ |
| Annual maintenance contract (rekeys, new hires, lost keys) | $500 – $2,000 per year |
Summary
A master key system is a hierarchy of keys and locks engineered with extra master wafers so that lower-level keys open only specific doors while higher-level (master) keys can open many or all doors — giving perfect convenience and access control when done with modern patented, restricted keyways.
