HydroLynx Technology
ALERT2: The Modern Standard for
Real-Time Flood Warning Telemetry
The current NHWC-governed protocol for automated flood warning networks — faster, more reliable, and built for the next generation of hydrologic monitoring.
Understanding the ALERT Protocol: A Foundation Built Decades Ago
For more than four decades, the Automated Local Evaluation in Real Time (ALERT) protocol has been the backbone of flood warning networks across the United States and beyond. ALERT made it possible for remote rain gauges, stream sensors, and weather stations to transmit data to central base stations during storm events — enabling emergency managers to issue timely warnings and protect lives.
But as the demands on flood monitoring networks have grown — more sensors, denser networks, higher-stakes decisions — the limitations of legacy ALERT have become increasingly apparent. The protocol operates at just 300 baud, supports only 8,192 unique sensor IDs, and uses a collision-based transmission method that results in data loss precisely when reliable data matters most: during a major storm event.
Enter ALERT2: The Next Generation
In 2010, the National Hydrologic Warning Council (NHWC) introduced ALERT2 as the official successor to legacy ALERT. Developed through the NHWC’s ALERT2 Technical Working Group (TWG), ALERT2 was designed from the ground up to overcome the technical limitations of its predecessor while maintaining a clear path for agencies to upgrade gradually.
ALERT2 is an open standard with no licensing fees or proprietary restrictions, meaning any manufacturer can build fully compliant, interoperable equipment. ALERT2 is a trademark of the National Hydrologic Warning Council (NHWC). HydroLynx’s full product line is ALERT2-compliant and interoperable with NHWC-certified equipment from other manufacturers.
ALERT vs. ALERT2: Side-by-Side Comparison
| Feature | Legacy ALERT | ALERT2 |
|---|---|---|
| Transmission Speed | 300 bps | More than 10× faster |
| Unique Site IDs | 8,192 sensor IDs | 65,000+ complete sites |
| Data Resolution | Integer only (0–2,047) | Full engineering values (floating-point) |
| Error Correction | None | Forward Error Correction (FEC) |
| Collision Handling | ALOHA — data loss risk | TDMA — time-synchronized, collision-free |
| Data Loss During Storms | Significant risk | Near-eliminated |
| Clock Synchronization | None | GPS-synchronized TDMA time slots |
| Protocol Architecture | Monolithic | Modern layered stack (extensible) |
| Backward Compatibility | N/A | Compatible with legacy ALERT networks |
| Open Standard | Yes (NHWC governed) | Yes (NHWC governed) |
How ALERT2 Works: Key Technical Concepts
Time Division Multiple Access (TDMA)
TDMA assigns each monitoring station a precise GPS-synchronized time window to broadcast. Unlike legacy ALERT, where multiple sensors could transmit simultaneously and corrupt each other’s data, TDMA eliminates contention entirely — dramatically improving reliability during major storm events when many sensors report simultaneously.
Forward Error Correction (FEC)
ALERT2 incorporates FEC into every transmission. The receiving base station can detect and correct errors in a message without requesting a re-transmission — reducing data loss and improving reliability even in poor radio conditions, when accurate data is needed most.
Expanded Network Capacity
Legacy ALERT networks in densely populated regions had nearly exhausted the available 8,192-sensor ID pool, making expansion impossible without costly workarounds. ALERT2 supports more than 65,000 complete monitoring sites — future-proofing networks for decades.
Rich, High-Resolution Data
Where ALERT was limited to integers between 0 and 2,047, ALERT2 supports full engineering-unit values with floating-point precision — more accurate rainfall totals, more granular water level readings, and richer meteorological data to support better decision-making during flood events.
Transitioning from ALERT to ALERT2
One of the most practical advantages of ALERT2 is that agencies do not need to replace their entire network at once. ALERT2-compliant encoders can capture legacy ALERT messages and retransmit them in ALERT2 format from existing repeater sites, allowing networks to transition gradually — station by station — according to budget and operational schedules.
Firmware Upgrade
Add the Model 5096/A2 ALERT2 encoder kit to compatible existing HydroLynx transmitters. Lowest cost, fastest path to ALERT2.
Transmitter Replacement
Replace the data transmitter with a new Model 50388/A2 or 50386/A2 — full ALERT2 capability in existing enclosures.
Packaged Station
Deploy a complete turnkey ALERT2 packaged station — sensor, transmitter, solar power, and enclosure, field-ready from the factory.
HydroLynx’s ALERT2 Product Line
HydroLynx Systems has built its entire current product line around the ALERT2 standard. Every packaged station, data transmitter, and receiver/decoder we manufacture is NHWC-compliant and interoperable with the broader ALERT2 ecosystem.
| Model | Description | Category |
|---|---|---|
| Model 50388 | ALERT2/SCADA Two-Way Transmitter | Data Transmitter |
| Model 50388/A2 | ALERT2 Data Transmitter | Data Transmitter |
| Model 50386 | Real-Time Two-Way Data Transmitter | Data Transmitter |
| Model 50386/A2 | ALERT2 Real-Time Data Transmitter | Data Transmitter |
| Model 5052RD-K-H | ALERT2 HDR Receiver/Decoder | Base Station Receiver |
| Model 5096/A2 | ALERT2 Firmware Upgrade Kit | Upgrade |
| Packaged Stations | Turnkey ALERT2 rain, water level, weather, and water quality stations | Packaged Systems |
Frequently Asked Questions
What is ALERT2?
How is ALERT2 different from legacy ALERT?
Do we have to replace our entire ALERT network at once?
Is ALERT2 an open standard?
Is HydroLynx equipment ALERT2 certified?
Planning an ALERT2 deployment or upgrade?
Our team has supported flood warning agencies through phased ALERT-to-ALERT2 transitions for decades. We can help you plan a migration that fits your budget, timeline, and existing network.
Request Information → Contact Our TeamHydroLynx Systems
830 Fesslers Pkwy, Suite #108
Nashville, TN 37210