How to Survey a Site for Wireless Alarm Signal Coverage: The Installer’s Guide

The alarm is armed. The installer has left. Two hours later the phone rings: a false alarm triggered by a sensor that lost contact with the hub, reconnected, and sent a tamper event.

Nine out of ten post-installation service calls for wireless alarm systems trace back to inadequate signal coverage during the planning phase. Not a hardware fault. Not a defective sensor. A signal path problem that should have been caught during a site survey.

This guide walks through a repeatable site survey methodology for wireless alarm installations—covering frequency planning, building material attenuation, hub placement, RSSI measurement with the RB Link app, and coverage mapping. The goal: one visit, one installation, zero return calls.

Why a Site Survey Is the Most Important Hour of the Installation

A wireless alarm system is only as reliable as the RF link between each sensor and the hub. Concrete walls absorb signal. Metal-framed windows reflect it. Water tanks and boiler rooms create dead zones. A site survey identifies these obstacles before any mounting brackets leave the van.

The cost of skipping this step is measurable. A 2025 analysis by the British Security Industry Association (BSIA) found that wireless alarm service calls driven by signal issues average 1.8 technician hours per visit, counting travel, diagnosis, re-mounting, and re-testing. At typical European Service Engineer day rates of €50 to €90 per hour, a single missed dead zone can cost more than the hardware it connects to.

A proper site survey takes 45 to 90 minutes depending on building size and complexity. It is the highest-ROI activity in the installation workflow.

868 MHz vs 2.4 GHz: Signal Planning Differences Every Installer Should Know

Wireless alarm systems in Europe operate primarily in two frequency bands. Understanding how each behaves in a building is the foundation of survey planning.

Practical implication for the installer: In a building with concrete or stone construction, an 868 MHz protocol such as Roombanker’s RBF Protocol will maintain a usable signal through 3 to 4 times more walls than a 2.4 GHz system before hitting the link margin floor. This means fewer repeaters, less cabling, and lower material cost for the same coverage area.

For a detailed comparison of protocol architectures, see Sub-GHz vs 2.4 GHz: Wireless Protocol Guide for Security Installers.

European Building Material Attenuation Reference Table

Signal loss through building materials varies significantly by frequency and construction type. The values below are derived from the ITU-R P.2040-3 recommendation (Effects of Building Materials on Radiowave Propagation) and validated against internal Roombanker field tests across 30 residential and commercial sites in Germany and Poland during 2025 Q2. These are typical values at normal incidence; actual loss depends on moisture content, material density, and angle of incidence.

How to use this table on site: Add the attenuation values for every barrier between the proposed hub location and each sensor position. If the total exceeds approximately 20 dB for a sub-GHz system or 15 dB for a 2.4 GHz system, consider repositioning the hub, adding a repeater, or selecting an alternative sensor placement. These are planning thresholds—final verification requires an on-site RSSI reading.

Pre-Installation Walkthrough: A Repeatable Site Survey Methodology

Step 1: Architectural Review (5–10 minutes)

Walk the building with the floor plan (or sketch one if none exists). Note:

• Wall construction materials for each major partition
• Location of concrete columns, lift shafts, stairwells with reinforced walls
• Service rooms containing boilers, water tanks, or large metal equipment
• Ceiling type (suspended vs solid) and underfloor spaces for cable routing
• Existing wireless equipment: Wi-Fi access points, cordless phone bases, other RF systems

Step 2: Hub Location Candidate Identification (10 minutes)

Identify two to three candidate positions for the alarm hub. Refer to the hub placement rules in the next section. Mark each candidate on the floor plan or with painter’s tape on the wall.

Step 3: Sensor Position Marking (10 minutes)

Mark each planned sensor position following the alarm design specification. At this stage, positions may still move depending on signal readings taken in Step 4.

Step 4: Signal Strength Measurement (15–30 minutes)

Using the RB Link app in signal test mode, place the hub temporarily at each candidate location and walk to each sensor position with a sensor or a signal test device. Record the RSSI reading at each point. Detailed RSSI interpretation is covered in the section below.

Step 5: Coverage Mapping (10 minutes)

Plot the RSSI values on the floor plan. Areas where signal drops below the usable threshold are marked as dead zones. Decide whether to relocate the hub, reposition sensors, or introduce a repeater.

Step 6: Final Hub Selection and Installation (10 minutes)

Select the hub location that provides the highest minimum RSSI across all sensor positions. Mount the hub, mount all sensors, and perform a final end-to-end test with all devices reporting.

How to Select the Hub Location: Six Rules

The hub is the single most important positioning decision in a wireless alarm installation. Move it two metres in the right direction and a marginal link becomes a solid one. These rules apply universally to sub-GHz and 2.4 GHz systems alike.

1. Place the hub centrally. The shortest path to the farthest sensor determines link reliability. A central location minimises the maximum distance. In a rectangular floor plan, the geometric centre is the starting point—adjust from there based on construction.
2. Mount at minimum 1.5 metres above floor level. At lower heights, furniture, appliances, and occupants absorb and scatter the signal. At 1.5 m or higher, the RF path clears most indoor obstacles. The ideal height range is 1.5 to 2.0 metres.
3. Maintain at least 50 cm distance from large metal objects. Metal columns, electrical panels, boiler housings, and server racks act as RF reflectors and absorbers. They create multipath nulls and standing wave patterns that cause unpredictable signal dropouts.
4. Avoid locating the hub on an exterior wall when possible. Mounting on an exterior wall radiates half the signal outside the building. If an exterior wall is unavoidable, the hub should face inward with the back toward the outside.
5. Keep the hub away from concrete columns and lift shafts. A reinforced concrete column with 400 mm of steel-reinforced concrete can attenuate a signal by 30+ dB at 868 MHz and 50+ dB at 2.4 GHz—effectively a brick wall in the RF path.
6. Do not place the hub inside a metal enclosure, cabinet, or utility room with large water tanks. Water is an efficient RF absorber at both frequency ranges. A storage tank between the hub and sensors creates a signal shadow that can be impossible to overcome without relocation.

How to Read RSSI Values in the RB Link App

The RB Link app includes a built-in signal strength indicator that displays the Received Signal Strength Indicator (RSSI) in dBm for each paired sensor. Understanding these readings is the core skill of site survey work.

RSSI Interpretation Table

How to Take a Reliable RSSI Measurement

Open the RB Link app and navigate to Device Settings > Signal Test. Place the hub in its proposed location and power it on. Walk to each sensor position holding the sensor at its intended mounting height. Trigger a test transmission from the sensor and read the RSSI value displayed in the app.

Critical note: Take the reading with the building in its normal occupied state. A concrete wall attenuates differently when it is dry versus rain-soaked. A room full of people absorbs more 2.4 GHz signal than an empty one. If the building will be occupied with furniture and people during normal use, the survey should reflect that.

For each sensor position, take three readings over 30 seconds and record the lowest value. This accounts for momentary fluctuations caused by people moving through the signal path or nearby electronic equipment cycling on and off.

Coverage Mapping and Dead Zone Identification

Coverage mapping is the practice of plotting measured RSSI values on a scaled floor plan to visualise signal distribution across the site. It transforms a set of point readings into a spatial understanding of the RF environment.

1. Draw or print a scaled floor plan showing all walls, doors, windows, stairwells, and major obstacles (columns, lift shafts, service rooms).
2. Plot the hub location as a central reference point.
3. Mark each sensor position with its measured RSSI value and rating colour:
   • Green (−30 to −75 dBm): Acceptable
   • Amber (−76 to −85 dBm): Marginal — flag for review
   • Red (below −85 dBm): Dead zone — requires mitigation
4. Identify contiguous dead zone areas. If three or more adjacent positions fall in the red zone, that part of the building has a systemic coverage problem. The cause is usually a dense obstacle (concrete core, service riser) between the hub and that zone.
5. Decide on mitigation. Options in order of preference:
   1. Relocate the hub to improve the path to the problem zone.
   2. Relocate the affected sensors to positions with better line-of-sight.
   3. Add an RF repeater at the boundary between the green zone and the dead zone.

Keep the annotated floor plan in the project file. It serves as documentation if signal issues arise during the system lifecycle and as reference for future expansions.

Real-World Field Examples

Example 1: Three-Floor Villa (Southern Germany)

Building: 280 m² total, reinforced concrete frame with aerated concrete infill walls, double-glazed windows with low-E coating. Hub proposed for ground floor living room.

Scenario: The installer planned 14 devices: 8 PIR motion sensors (indoor), 3 door/window magnetic sensors, 1 outdoor alarm siren, 1 keypad, 1 smoke detector. The master bedroom sensor on the first floor sat directly above the hub, one floor up, with a reinforced concrete slab between them.

Survey result: Ground floor devices all measured −55 to −70 dBm — well within the green zone. First-floor devices read −65 to −80 dBm. The attic smoke detector read −92 dBm through the roof slab construction. The installer relocated the hub from the living room to a hallway cupboard at the centre of the ground floor, reducing the path to the attic by 4 metres and removing a concrete column from the signal path. The attic reading improved to −78 dBm. Total survey time: 55 minutes.

Example 2: 200 m² Apartment (Bucharest, multi-storey block)

Building: 1960s reinforced concrete apartment, 200 m², single floor, exterior walls 400 mm reinforced concrete. Interior partitions are brick with plaster finish. The apartment is on the 7th floor of a 12-storey block.

Scenario: 10 devices including PIR sensors in each room, two door sensors (main entrance plus terrace door), one keypad near the entrance, one water leak detector in the bathroom.

Survey result: The bathroom water leak detector read −93 dBm because the signal passed through a concrete column next to the bathroom door at nearly grazing incidence. The installer moved the sensor from the floor (behind the WC) to the wall beside the washbasin, adding 40 cm of clearance from the column edge. RSSI improved to −74 dBm. No repeater needed. Total survey time: 40 minutes.

Example 3: Small Office (Warsaw, converted historic building)

Building: 120 m² ground-floor office in a converted 19th-century tenement. External walls: 500 mm solid brick. Internal partitions: timber frame with plasterboard. Double-glazed windows (standard, no low-E coating). Suspended ceiling with 60 cm plenum space.

Scenario: 6 PIR sensors, 3 door sensors, 1 keypad, 1 indoor alarm siren. The client requested no visible wiring and minimum disruption to the finished interior.

Survey result: The main challenge was the 500 mm brick exterior walls, which attenuated the signal by 22 dB at 868 MHz per wall. The hub was placed in a central corridor at 1.6 m height. All interior sensors within the timber-and-plasterboard partitions read −50 to −70 dBm. The two sensors in rooms near the building perimeter passed through one brick wall each and measured −78 dBm and −82 dBm—both acceptable. No repeaters required. Total survey time: 30 minutes.

Frequently Asked Questions About Wireless Alarm Site Surveys

How far can the RBF Protocol transmit through concrete walls?

In internal testing across 30 residential and commercial sites in Germany and Poland (2025 Q2), RBF Protocol at 868 MHz maintained a usable signal through up to three 200 mm reinforced concrete walls at typical residential distances before reaching −85 dBm. Exact performance depends on wall spacing, angle of incidence, and moisture content of the concrete. A dedicated range test across 50 European sites covers this in detail.

Can I rely on the hub placement guide in the product manual instead of doing a site survey?

The product manual provides general placement guidelines, but it cannot account for the specific construction of each building. A building from the 1960s with reinforced concrete frame performs differently from a 2010s timber-frame structure. The 45 minutes spent on site survey is the only way to verify that the generic rules actually apply to the specific building.

What is the minimum RSSI required for EN 50131 Grade 2 compliance?

EN 50131 does not define a specific RSSI threshold. It requires that the alarm system maintain reliable communication under normal operating conditions. Industry best practice for Grade 2 installations treats −85 dBm as the planning limit for intrusion devices and −75 dBm for life-safety devices. For a full breakdown of Grade 2 requirements, see the EN 50131 Grade 2 Wireless Compliance Guide.

Do I need different survey equipment for 868 MHz vs 2.4 GHz systems?

The RB Link app works with any Roombanker hub and displays RSSI for both RBF Protocol (868 MHz) devices and any Wi-Fi/IP devices operating on 2.4 GHz. No additional equipment is needed beyond the hub and a test sensor. For third-party systems, a handheld spectrum analyser covering the relevant frequency band is useful for identifying interference sources.

How does a metal roof or metal roof insulation affect signal?

Metal roof decking, metal-clad insulation panels, and foil-backed insulation blankets are among the most challenging obstacles for wireless signals. A continuous metal surface can attenuate both 868 MHz and 2.4 GHz signals by 30 dB or more. In buildings with metal roofs, the hub must be positioned below the roofline and sensors placed so the signal path does not intersect the metal surface at a shallow angle. In extreme cases, a separate hub or repeater may be needed for attic or loft spaces.

Should I survey the site before or after running cables?

Before. The site survey tells you where the hub needs to be. Cabling decisions (power to the hub, ethernet backhaul to the router, wiring for wired sensors) follow from that location. Running cables first and then discovering that the natural cable termination point is an RF dead zone results in wasted labour and compromised system performance.

What causes sudden signal degradation months after installation?

Environmental changes are the most common cause. A new metal filing cabinet in an office, a refrigerator installed against the wall shared with the hub, or seasonal moisture changes in brick walls can shift RSSI by 3 to 8 dB. Seasonal re-testing during annual maintenance is the recommended practice: walk each sensor, check its RSSI in the RB Link app, and note any drift compared to the baseline survey readings.

Download the Site Survey Checklist

A pre-printed checklist ensures consistency across every installation. The Roombanker Site Survey Checklist PDF covers: pre-visit documentation review, walkthrough steps, hub candidate evaluation, RSSI recording template with colour-coded floor plan, dead zone decision matrix, and final acceptance sign-off. Each item is field-tested and designed to be completed during the survey visit, not from memory afterward.

Download the Site Survey Checklist PDF

For installers working with Roombanker equipment, the engineering team offers remote survey support for complex sites. Contact the Roombanker engineering team for a consultation.

Summary for Installers

• A site survey takes 30 to 90 minutes and eliminates the most common cause of post-installation service calls.
• 868 MHz sub-GHz protocols (including RBF Protocol) penetrate concrete and stone 2 to 3 times better than 2.4 GHz at the same power level.
• Use the ITU-R P.2040-3 material attenuation table as a planning reference, but always verify with on-site RSSI measurements.
• The hub location is the single most impactful decision. Central, 1.5 m minimum height, away from metal and water.
• Record and annotate all RSSI values on a floor plan. This baseline documentation saves hours during maintenance visits.
• The RB Link app provides all the measurement capability needed for a professional site survey—no additional equipment required.

First published: May 2026. Part of the Roombanker Installation Best Practices series.

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