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How does RTLS actually work, and what does each architecture require?

By Thaddeus Stepanovich — Founder, Harbinge.rs · 14 years in EMS and healthcare IT

What are the main RTLS architectures?

Five underlying technologies account for nearly every hospital RTLS deployment on the market today. Each makes a different trade between locating precision, coverage cost, and how much new infrastructure it demands.

The pattern across the table: the tighter the accuracy claim, the more physical infrastructure — and the more of it — a vendor needs in your ceilings and walls.

How do IR and ultrasound systems achieve room-level certainty?

Infrared and ultrasound both share a useful physical property for healthcare locating: neither signal passes through walls. That means a receiver in a room only hears tags that are actually in that room, which is what lets these architectures claim "certainty-based" accuracy rather than a probabilistic estimate.

CenTrak describes its Gen2IR™ (Second Generation Infrared) as "the gold standard for certainty-based, room- and bay-level locating in clinical environments," filtering out interference from sunlight and fluorescent lighting and detecting tags even under blankets or clothing. For spaces that don't have physical walls — open bays in the ER, PACU, or infusion areas — CenTrak's "Virtual Walls" feature and its IRUS™ hybrid (Ultrasound + Gen2IR) product line are built specifically to draw sub-room-level boundaries in open clinical layouts.

Sonitor's approach centers on Ultrasound Low Energy (ULE): ceiling-mounted ultraBeacons transmit 40 kHz and 20 kHz acoustic signals that Sonitor tags and partner devices detect. Because ultrasound is room-bounded the same way infrared is, Sonitor markets ULE as delivering sub-room and room-level location certainty, combined in its SonitorONE platform with BLE, RFID, GPS, and mobile-device tags for broader workflow coverage. Sonitor's materials describe ULE as avoiding some of the interference and infrastructure burden common in other RTLS types — a vendor claim worth weighing against its own competitors' equivalent claims, since no independent lab has benchmarked the comparison.

How do BLE and Wi-Fi systems trade accuracy for coverage?

BLE and Wi-Fi architectures give up wall-bounded certainty in exchange for cheaper, faster-to-deploy coverage — in some cases reusing network hardware that's already installed.

CenTrak's BLE locating option is positioned as "near-room level certainty" with location updates every 15–20 seconds, which CenTrak frames as balancing accuracy, reliability, affordability, and efficiency against its room-certain IR line. Facilities can reuse existing Wi-Fi or BLE-enabled access points rather than installing a dedicated network. AiRISTA's Sofia® platform takes a similar multi-radio approach, combining RFID, BLE, and Wi-Fi in one system; its hardware lineup includes a BLE Angle-of-Arrival Gateway (a sub-1-meter accuracy claim under favorable conditions), a BLE Beaconing Gateway Unit, and a Wi-Fi/BLE Gateway that bridges BLE tags onto an existing 2.4/5 GHz Wi-Fi network to extend coverage without a parallel physical build-out.

Zebra sits at the accuracy end of this same trade-off spectrum with its UWB offering under the MotionWorks software portfolio: a UWB Hub on standard Cat5e/PoE Ethernet supports up to 64 sensors and roughly 3,500 tags reporting at 1 Hz, with line-of-sight sensor range up to 200 meters and accuracy Zebra states as typically better than 30 cm — markedly tighter than the 1–3 meter range typical of BLE zone-level systems. That precision requires its own dedicated sensor network rather than riding on existing Wi-Fi, which is the infrastructure cost of buying back the accuracy that BLE and Wi-Fi architectures trade away.

Where do the costs actually live?

Vendors rarely publish list pricing for hospital RTLS — CenTrak, Sonitor, and AiRISTA all direct buyers to a sales conversation rather than a price sheet — but the cost structure follows the same four buckets regardless of which architecture you choose.

• Hardware. BLE infrastructure is generally the cheapest tier — one industry analysis puts BLE RTLS hardware at "several tens of dollars per piece" versus "several hundreds of dollars" for other RTLS hardware types, framing it as up to roughly 90% lower per-unit cost, though treat that figure as directional rather than audited. UWB sits at the opposite end: precision hardware like Zebra's hub-and-sensor network is a purpose-built system, not a repurposed access point.
• Installation labor. This is the line item that tends to surprise buyers, because it happens in occupied clinical space — ceiling access, cabling runs, and coordination around patient care hours. Vendors are responding with battery-powered options to cut it down: CenTrak's DualTrak infrastructure reaches 10+ years of battery life at a 3-second update rate and requires no wiring, and Sonitor's materials describe its ceiling-mount transmitters as clipping into a standard drop-ceiling grid without cabling. Both claims are worth confirming against your own facility's ceiling type during a site walk.
• Tags and batteries. Every tracked asset needs its own tag, and every tag needs a battery someone eventually replaces. AiRISTA states its non-disposable BLE tag battery life "can easily range from 2 to 5+ years" depending on update frequency and duty cycle; CenTrak's newer dry-cell tags claim 10+ years under specific conditions. These figures use different test assumptions across vendors and aren't apples-to-apples — budget for an ongoing battery-management program, not a one-time purchase.
• Recalibration and maintenance. Environmental monitoring tags in particular typically need annual recalibration to meet NIST requirements, and any deployment covering thousands of tags across pumps, beds, and wheelchairs needs a standing process for battery swaps and firmware updates, not just an initial rollout.

Because these costs compound differently over a system's life, industry guidance is to request a five-year total-cost-of-ownership model from a vendor rather than a per-tag quote. See what RTLS actually costs per bed for a fuller breakdown of how these four buckets add up in practice.

When is RTLS the right answer?

RTLS earns its infrastructure when the use case genuinely needs continuous, real-time location — not a periodic check. Emergency department throughput management, where staff need to see bed and bay status the instant it changes, is a canonical fit. So is active wander management for at-risk patients, where a delay of minutes matters. Staff duress monitoring and hand-hygiene or rounding compliance tracking also depend on the system knowing where someone is right now, continuously, which is exactly what fixed infrastructure and always-on tags are built to do.

If your actual problem is knowing where an asset was as of the last time someone was near it — for inventory, audit, or compliance reporting rather than moment-to-moment operations — that continuous-tracking guarantee is more infrastructure than the problem requires.

Where Forager fits

Forager is built for the adjacent problem RTLS wasn't designed to solve cheaply: confirming where an asset is, on a recurring basis, without installing readers, running cable, or maintaining a tag battery on every device. It piggybacks location confirmation onto work your team already does — a tech walking past with a phone, a badge tap, a routine round — rather than requiring dedicated locating infrastructure in every room.

That trade-off means Forager doesn't attempt continuous real-time locating the way CenTrak, Sonitor, Zebra, or AiRISTA do — if your use case is active wander management or second-by-second ED throughput, RTLS is the right tool. But for asset inventory, compliance attestations, and audit-ready location history across a large equipment fleet, Forager delivers confirmed location at $15/device/yr with no ceiling work and no per-tag battery program to run. See RTLS alternatives for a fuller comparison, or go straight to how Forager works.