Electrical Craft Practice: Intruder and Fire Alarm Systems

Comprehensive vocabulary flashcards covering intruder alarm circuits, sensor technologies, zoning, IS 199 standards, signalling, and fire alarm systems based on Phase 6 Electrical Craft Practice.

Intruder Alarm System

An electrical installation designed to detect and signal the unauthorized presence, entry, or attempted entry of an intruder into a protected premises.

Control Panel

The central processing hub or 'brain' of an alarm system, containing a printed circuit board with a microprocessor, a standby backup battery, and connection terminals for field detection devices, keypads, and sounders.

Remote Keypad (RKP)

A digital user interface used to arm, disarm, and program the alarm system, enter user codes, and access installer engineer mode for diagnostic testing.

Normally Open (NO) / Open Loop System

An alarm circuit configuration where detection contacts are wired in parallel and remain open in the non-alarm state; closing any contact completes the circuit to energize an alarm relay, but a severed cable leaves the system completely bypassed without warning.

Normally Closed (NC) / Closed Loop System

The preferred alarm wiring configuration where detector contacts are wired in series and remain closed under normal conditions, sustaining a continuous monitoring current to a relay; opening a contact or severing the cable drops the relay to trigger an alarm.

End-of-Line (EOL) Resistor

A fixed resistor installed at the furthest point of a detection circuit that provides a defined loop impedance, enabling the panel to differentiate between an intact circuit, an open-circuit intrusion, and a short-circuit tamper attempt.

Tamper Circuit

A supervised 24-hour monitoring loop that detects physical interference, cover removal via internal microswitches, or severed wiring, sounding internal sounders when unset and initiating a full alarm condition when armed.

Diode-Shunted Window Circuit

A monitoring circuit where normally closed contacts are shunted by individual diodes; monitoring current flows through the forward-biased diodes when unset (allowing windows to open without alarm), while polarity reversal when armed reverse-biases the diodes, forcing current through the contacts so opening a window triggers an alarm.

Magnetic Reed Switch Contact

A perimeter detection device consisting of a reed switch mounted on the static frame and a permanent magnet mounted on the moving sash or door; opening the opening draws the magnet away, opening the reed contacts to trigger an alarm.

Inertia Sensor (Shock Sensor)

A shell protection device comprising a gold-plated ball seated across two contact pins; physical impact or forced vibration dislodges the ball, momentarily breaking the circuit and registering an attack pulse at the control panel.

Pulse Count

A programmable panel setting (typically 1 to 9) that dictates how many discrete impact pulses an inertia sensor must register within a set window before triggering a full alarm, preventing false alarms caused by wind or traffic.

Vibration Detector (Leaf Spring Type)

A mechanical sensor consisting of a vertically mounted leaf spring suspended at its top end with an attached weight and moving contact at its bottom end; shock waves separate the moving contact from a fixed casing contact to generate an alarm signal.

Passive Infra-Red (PIR) Detector

A trap protection sensor that detects motion by focusing infrared thermal radiation onto a pyroelectric element through a Fresnel lens; an alarm is triggered when a moving body crosses its optical zones at an angle.

Pet Immunity

A signal-processing feature in passive infrared detectors that ignores infrared heat signatures and mass thresholds characteristic of small domestic animals, avoiding false alarms without requiring physical masking of detection beams.

Active Infra-Red (IR) Beam

A point-to-point barrier detector consisting of an optical transmitter directing a continuous modulated infrared beam across an open span to an opposing receiver, activating an alarm when an intruder interrupts the beam path.

Ultrasonic Detector

A volumetric motion detector that radiates high-frequency sound waves above $30\,\text{kHz}$ into a room and monitors reflected wave patterns; moving objects induce a frequency shift via the Doppler effect to trigger an alarm.

Acoustic Glass Break Detector

A shell protection device equipped with a microphone and microprocessor filter tuned to detect the characteristic high-amplitude shock and flexural fracture frequencies ($3\text{--}5\,\text{kHz}$) of shattered architectural glass.

Pressure Mat

A trap protection device consisting of two flexible conductive metal plates separated by an insulating matrix or high-resistance globules; applied foot pressure bridges the plates together to close a normally open contact circuit.

Panic Button (Personal Attack / PA)

A manually triggered hand or foot switch comprised of key-latched contacts; pressing the button immediately generates a duress alarm on a 24-hour monitored circuit regardless of whether the system is set or unset.

Perimeter Protection

The outer boundary security layer designed to detect unauthorized physical presence crossing site boundaries, fencing, or approach gates before reaching a structure (e.g., long-range microwave beams).

Shell Protection

The security layer defending the exterior structural fabric, walls, and entry portals of a building using magnetic contacts, inertia vibration sensors, and acoustic glass break detectors.

Trap Protection

The internal volumetric defense layer designed to detect intruder movement inside hallways, staircases, and corridors after building penetration (e.g., PIRs and pressure mats).

Zoning

The division of an alarm installation into distinct electrical sectors to permit independent arming (part set), provide immediate visual location of an activation, and narrow down the source of circuit faults.

Exit/Entry Zone

A programmable, timed detection zone covering an access doorway that initiates a countdown allowing authorized occupants to depart or enter and disarm the system before reverting to an active alarm loop.

24-Hour Zone

A continuously monitored circuit that remains fully active at all times, generating an internal warning tone when unset and initiating a full external alarm and remote notification when armed.

Duress Signalling

A silent or audible distress signal sent to a central monitoring station, triggered either by activating a dedicated panic button or by inputting a specialized disarm duress code into the keypad under coercion.

Walk Test

A diagnostic routine selected at the control panel enabling an installer or occupant to test every sensor without activating external sirens, verifying operation through audible chimes and panel zone indicators.

Self-Activating Bell (SAB)

An exterior siren housing fitted with an internal rechargeable backup battery and a hold-off relay; if the external supply or field cable is severed, the relay drops out and connects the onboard battery to sound the siren.

Bell Timeout

A statutory environmental restriction mandated by standard IS 199 requiring external intruder sounders to automatically silence after a minimum duration of $15\,\text{minutes}$ and a maximum duration of $30\,\text{minutes}$.

Digital Communicator

A signaling module integrated into the panel that connects to telephone lines or cellular networks to transmit coded event messages to designated telephone numbers or a remote alarm receiving centre.

Central Monitoring Station (ARC)

A secure, continuously manned facility that receives telemetry and duress alarm signals from subscriber installations to initiate formal response actions, such as dispatching keyholders or contacting Gardaí.

Shunt Lock

A key-operated high-security lock mechanism fitted with an electrical bypass switch, allowing authorized personnel to access a door by temporarily isolating its detection contacts without setting off the alarm.

Anti-Tamper Device

A closed-circuit switching device designed to create an alarm condition whenever an access door, lid, or enclosure of security equipment is opened via its normal method of opening.

IS 199 Specification Limits

Irish intruder installation rules specifying a maximum of $12$ detection devices per zone, a maximum of $3$ devices on an exit/entry zone, a maximum of $1$ PIR per zone, $12\,\text{hours}$ of battery backup, and a minimum siren sound level of $70\,\text{dB(A)}$ at $3\,\text{metres}$.

Door Intercom System

A low-voltage or SELV communication system comprising an indoor telephone handset, an outdoor entry panel with call push and speech transmitter, and an electric solenoid door-release mechanism operating typically at $12\,\text{V AC}$.

Uninterruptible Power Supply (UPS)

An electrical power buffer unit that conditions line voltage and provides continuous battery-backed power during mains failures to prevent data corruption or shutdown of sensitive computer loads.

Manual Call Point (MCP)

A manual fire alarm initiating device installed along escape corridors and exits at a height of $900\text{--}1,200\,\text{mm}$ with a maximum travel distance of $30\,\text{metres}$, which latches its switch contacts to trigger an alarm.

Addressable Fire Alarm System

A fire detection loop architecture where the control panel polls individually identified field devices over a shared two-wire loop, pinpointing the exact identity and physical location of an operated sensor.

Short-Circuit Isolator

A line-protection module installed along an addressable fire loop that automatically disconnects a shorted section of cable, allowing the unaffected devices to maintain communication from both directions.

Category M Fire System

A fire alarm installation classification that relies entirely on manual initiation via manual call points without incorporating automatic fire detection.

Category L1 Fire System

A comprehensive life protection fire alarm system category requiring automatic fire detection installed throughout all rooms and circulation areas of a building.

Category L3 Fire System

A life protection category providing automatic fire detection installed along all designated escape routes and within all rooms opening directly onto those routes.

Optical (Photoelectric) Smoke Detector

A fire sensor utilizing the light-scattering principle, where smoke entering a dark chamber deflects an infrared LED beam onto a photocell; highly sensitive to visible smoke from smouldering fires.

Ionisation Smoke Detector

A fire sensor containing a small radioactive source that ionizes chamber air to maintain a minute current; entry of invisible combustion aerosols drops the current, making it ideal for fast-flaming fires.

Rate-of-Rise Heat Detector

A thermal sensor containing an exposed and a shielded temperature-sensing element; rapid temperature increases cause the exposed element to expand faster and close alarm contacts, while slow ambient heating is dissipated.

Fire Alarm Sounder Circuit Supervision

A monitoring technique that continuously passes a reverse-polarity extra-low-voltage current through an end-of-line resistor ($6.8\,\text{k}\Omega$) blocked by series diodes at each sounder, switching to forward polarity during a fire condition to operate the sounders.

Fire Stopping

The installation of certified non-combustible sealing materials around cable and service penetrations passing through fire-rated compartmental walls or floors to reinstate the structural fire resistance.

Diversity (Electrical)

The calculated mathematical ratio of the maximum electrical power demand of an installation to its total connected load, used to determine appropriate cable sizes and circuit protective device ratings.