Mantrap Interlock Portal Product

Overview

A mantrap interlock portal (or mantrap airlock) is a physical security system consisting of two interlocked doors separated by a small buffer space (the trap). The interlock logic ensures that both doors cannot be open simultaneously: if someone opens the outer door to enter the trap, the inner door is locked; after the person closes the outer door, an [[mantrap-interlock-occupancy-sensor|occupancy sensor]] confirms the person is alone in the trap, and only then does the system unlock the inner door for exit.

Mantraps are deployed in high-security facilities where "man-trap" attack (two people attempting to enter through one access event) is a known threat. They are found in server rooms, vaults, executive suites, classified government buildings, and research laboratories. A mantrap forces each person to enter one at a time and requires each person to present a valid credential at both the entry (outer) and exit (inner) points, preventing piggybacking and unauthorized tailgating.

The system also serves as a "credential exchange zone": a visitor can stand in the trap, provide identification and purpose to a [[mantrap-interlock-intercom|building representative via intercom]], receive authorization, and only then be allowed to proceed into the secure area.

How it works

The [[mantrap-interlock-control-logic|control logic module]] enforces a strict state machine:

READY state: Both outer and inner doors are closed. The outer [[mantrap-interlock-door-position-sensors|door sensor]] shows CLOSED. The inner [[mantrap-interlock-door-position-sensors|door sensor]] shows CLOSED. The [[mantrap-interlock-occupancy-sensor|occupancy sensor]] shows EMPTY. Both doors are locked.

OUTER OPEN: A cardholder swipes their badge at the outer door's card reader. The [[access-control-panel|access panel]] authorizes them and sends a relay signal to unlock the [[electric-strike|outer electronic strike]]. The cardholder pulls the outer door open. The [[mantrap-interlock-door-position-sensors|outer door sensor]] changes to OPEN. Simultaneously, the [[mantrap-interlock-control-logic|MCU]] verifies that the [[mantrap-interlock-door-position-sensors|inner door sensor]] is still CLOSED, and locks the inner [[magnetic-lock|magnetic lock]].

TRAP OCCUPIED: The cardholder steps into the trap volume. The [[mantrap-interlock-occupancy-sensor|occupancy sensor]] (PIR motion detector or pressure mat) detects motion/weight and signals OCCUPIED. The [[mantrap-interlock-control-logic|MCU]] notes this state.

OUTER CLOSED: The cardholder closes the outer door behind them. The [[mantrap-interlock-door-position-sensors|outer door sensor]] changes back to CLOSED. The [[electric-strike|outer strike]] re-locks.

DWELL TIME: The [[mantrap-interlock-control-logic|MCU]] waits for a dwell timer (typically 2–5 seconds). This allows any followers attempting to piggyback to fully commit to the trap before it locks. If a second person is detected by a pressure mat, the timer restarts.

TRAP EMPTY: The cardholder exits through the inner door. As soon as the [[mantrap-interlock-occupancy-sensor|occupancy sensor]] detects the person has left the trap, the sensor output returns to EMPTY.

INNER UNLOCK: Once the sensor confirms EMPTY and the dwell timer expires, the [[mantrap-interlock-control-logic|MCU]] energizes the [[magnetic-lock|inner magnetic lock]] release solenoid. The inner door is now unlocked and the cardholder can push through into the secure area.

INNER CLOSED: The cardholder closes the inner door. The [[mantrap-interlock-door-position-sensors|inner door sensor]] shows CLOSED, and the [[magnetic-lock|inner lock]] re-locks. The system returns to READY state.

If at any point both door sensors read OPEN simultaneously, the [[mantrap-interlock-control-logic|MCU]] immediately triggers the [[mantrap-interlock-alarm-siren|alarm siren]] and sends an alert to security. This violation indicates a forced-entry attempt or a system failure.

Occupancy sensing and antipassback

The [[mantrap-interlock-occupancy-sensor|occupancy sensor]] is critical to the system's security. It must reliably detect a single person in a trap volume of 1.5–2.5 m depth × 1.2–1.5 m width. There are two common approaches:

PIR Motion Detector: A [[hall-sensor|pyroelectric infrared sensor]] detects body heat. The sensor is mounted at 0.3 m above the floor (at chest height) and has a narrow field of view focused on the trap center. The sensor's 100 ms response time is fast enough to detect a moving person. However, a person who stands perfectly still for >30 seconds (uncommon but possible) may not be detected. As a backup, a pressure-sensitive floor mat under the carpet provides a secondary occupancy signal.

Pressure Mat: A [[pressure-sensor|floor-mounted pressure-sensitive mat]] under the trap floor detects any weight >10 kg (to avoid false triggers from moving air or animals). The mat is more reliable than PIR in all environmental conditions. However, pressure mats wear over time and require periodic replacement (every 2–3 years).

Modern systems use both sensors in redundant configuration: PIR for speed, pressure mat for reliability. The [[mantrap-interlock-control-logic|MCU]] requires BOTH sensors to confirm EMPTY before unlocking the inner door.

Credential exchange and visitor management

Many mantraps include a [[mantrap-interlock-intercom|two-way intercom system]] with an external camera. A visitor without a badge can press a call button outside the outer door. The [[mantrap-interlock-intercom|camera]] displays the visitor's image to a receptionist or security officer inside the building. The receptionist can speak with the visitor via [[mantrap-interlock-intercom|two-way audio]], verify their identity and purpose, and if authorized, press a button to remotely unlock the outer door (after verifying no one else is in the trap).

This credential exchange method is slower than badge swipe (20–30 seconds vs. 2–3 seconds) but is essential for visitor entry and for people who have lost or forgotten their badge. The video record of visitors also provides a security audit trail for investigating unauthorized entry attempts.

Alarm and policy violations

The [[mantrap-interlock-alarm-siren|alarm siren]] is triggered if:

1. Both doors open simultaneously: Indicates forced entry or system failure. The [[mantrap-interlock-door-position-sensors|door sensors]] report both OPEN at the same time. Alarm sounds immediately.

2. Person trapped for extended duration: If the [[mantrap-interlock-occupancy-sensor|occupancy sensor]] reports OCCUPIED for more than 30 seconds without the door opening, the system assumes the person is stuck or in distress. Alarm sounds and a notification is sent to security/building management.

3. Inner door forced open while occupied: If the [[mantrap-interlock-door-position-sensors|inner door sensor]] opens while [[mantrap-interlock-occupancy-sensor|occupancy sensor]] reads OCCUPIED (without going through outer-close-dwell sequence), the [[mantrap-interlock-control-logic|MCU]] detects a policy violation. Alarm sounds.

4. Multiple persons detected: If a [[pressure-sensor|pressure mat]] detects more than one person's weight at once, the system triggers an alarm (attempted piggybacking).

The alarm is visual and audible:

• Audible: A piezo siren or electronic speaker sounds at 85+ dB, audible throughout the facility.
• Visual: Red alarm beacon mounted inside and outside the trap flashes at 1–2 Hz. A red "UNAUTHORIZED ENTRY ATTEMPT" message may display on LED signage.
• Alert notification: The [[mantrap-interlock-control-logic|MCU]] or integrated access control system sends an alert to security personnel's phones and the central monitoring station.

Emergency egress

Life-safety codes (e.g., NFPA 101) require that even a mantrap cannot trap a person indefinitely if there is a power loss or system failure. The inner door must have a manual mechanical override: a hardened steel pad (push-to-exit lever) that mechanically disengages the lock, allowing the person to push the door open and exit.

Some systems include a "fire alarm release": if the building fire alarm is triggered, a relay closes that energizes all door strikes and magnets, unlocking all doors (including the inner mantrap door) to allow rapid evacuation.

In a true emergency (medical, security breach), building management can press a "panic unlock" button on the main security console, which remotely energizes all door locks and sends an emergency unlock signal to the mantrap system.

Installation and commissioning

The mantrap trap volume must be sized correctly to prevent overcrowding and to ensure occupancy sensors can reliably detect a single person. Typical dimensions are:

• Depth: 1.5–2.0 m (allows a person to fully close the outer door before reaching the inner door)
• Width: 1.2–1.5 m (matches standard hallway width)
• Height: 2.4 m (standard ceiling height, allows airflow and prevents claustrophobia)

The [[mantrap-interlock-door-position-sensors|door position sensors]] must be carefully calibrated. A misaligned sensor can cause the inner door to unlock before the outer door is fully closed, compromising security.

The dwell timer (time between outer-close and inner-unlock) should be adjusted based on facility policy:

• Short dwell (1–2 seconds): Faster user experience, but allows quick piggybacking if a follower is very fast.
• Long dwell (5–10 seconds): Slower user experience, but any follower has time to fully commit to the trap and be detected by occupancy sensor.

Most facilities use 3–5 seconds as a middle ground.

Maintenance and monitoring

The [[mantrap-interlock-occupancy-sensor|PIR occupancy sensor]] must be kept clean; dust on the lens reduces detection range. Monthly cleaning with lens cleaning solution restores performance.

The [[pressure-sensor|pressure mat]] accumulates dirt and degradation. The mat should be tested monthly (walk across it to verify it detects), and replaced every 2–3 years.

The [[mantrap-interlock-door-position-sensors|door position sensors]] (reed switches) should be tested monthly to verify they reliably detect the door fully open and closed.

The [[mantrap-interlock-alarm-siren|alarm siren]] should be tested monthly (brief test at reduced volume to avoid disturbing building occupants).

The [[mantrap-interlock-intercom|intercom system]] should be tested weekly to ensure clear audio and visible video feed.

The [[mantrap-interlock-control-logic|MCU]] logs all trap events (door open, door close, occupancy detect, alarm trigger) to an audit log. The log should be reviewed daily by security personnel to identify trends (frequent alarms, stuck doors, sensor failures).

Security considerations

A well-designed mantrap is nearly impossible to defeat, but several attack vectors have been observed:

Weapon concealment: An attacker can hide a weapon in the trap after exiting, then retrieve it later. Mitigations include CCTV monitoring, random physical inspections of the trap, and pressure-sensitive floor mats that alert on object placement.

Sensor spoofing: An attacker with knowledge of the system might place a heat source or weight to fool the occupancy sensor. Redundant sensing (PIR + pressure mat) makes this harder.

Forced entry during transition: An attacker can attempt to force the inner door open while the outer door is still closing. Hardwired relay logic (vs. software-based MCU logic) is more tamper-proof; relay logic guarantees the inner lock remains energized while the outer door is opening or closing.

Power failure and manual override: If an attacker can cut power, the inner door manual emergency exit becomes available. However, manual exit is noisy and typically monitored.

Most high-security installations pair the mantrap with CCTV coverage, security personnel monitoring, and incident response procedures to detect and respond to any attempted compromise.