Do you need two SIM cards from two different carriers?

This is highly recommended. Having two SIM cards from the same carrier does not protect against a carrier outage (core network, regional BTS outage). With two different carriers (e.g., Orange and SFR), the probability of both experiencing an outage at the same time is virtually zero. Multi-carrier M2M SIM cards (a single SIM that accesses multiple networks) offer an effective alternative.

How does automatic failover work?

The router continuously monitors the quality of the primary SIM connection (ping to a reference server, RSRP, signal quality). If the connection is lost or degrades below a configured threshold, the router switches to the secondary SIM. Active sessions (VPN, MQTT) reconnect automatically. The failover time ranges from 10 to 60 seconds, depending on the implementation.

Can both SIM cards work at the same time?

In most industrial routers, active/passive mode (one SIM at a time) is the standard. Some high-end routers support active/active mode (load balancing between the two SIMs), but this requires SIMs with different cost tiers and a more complex configuration. For standard industrial IoT, active/passive mode is more than sufficient.

How can I monitor the status of both SIM cards remotely?

Through the cloud-based fleet management platform, the active operator, the signal strength (RSRP/RSRQ), the number of handoffs, and connectivity incidents are reported in real time. Alerts can be configured if the number of handoffs over a 24-hour period exceeds a threshold (indicating unstable coverage).

High Availability

Dual-SIM 4G Router: Guaranteed Service Continuity

Industrial dual-SIM 4G router: automatic failover between two carriers, zero downtime at your critical sites. How it works, use cases, and selection criteria.

Quick answer

A dual-SIM 4G router (dual SIM) features two slots for M2M SIM cards, ideally from two different carriers. In active/passive mode: the primary SIM maintains the connection, while the secondary SIM automatically takes over in the event of signal loss, a carrier outage, or if a latency threshold is exceeded. The switchover is transparent to connected devices and typically occurs in less than 60 seconds.

Why Dual SIM Is Essential at Critical Sites

A 4G router with a single SIM card is vulnerable to a single point of failure: an operator outage, a BTS antenna overload, or a simple local coverage issue. At a critical site (such as a pumping station, power substation, or production facility), a 2-hour outage can cost thousands of euros.

The dual-SIM 4G router eliminates this risk:

Carrier independence — two separate networks, two SIM cards.
Automatic failover — no human intervention required.
Application transparency — VPN, MQTT, and remote access connections automatically reconnect.
Network status monitoring — see in real time which SIM is active and why.

Dual-SIM Architecture

Failover Configuration Criteria

RSRP Signal Typical switch-over threshold: -115 dBm RSRP. Below this threshold, the connection is too unstable for an industrial VPN. The system switches to the secondary SIM.

Connectivity Test (ping) A ping is sent every 30 seconds to a reference server. If 3 consecutive pings fail → failover. More reliable than a simple signal indicator (an antenna may be connected but not routing Internet traffic).

Latency If latency consistently exceeds 500 ms (network congestion) → optional failover.

Automatic Switchback When the primary SIM regains a strong signal, the router switches back to it after a stabilization period (e.g., 5 minutes of stable signal) to prevent signal fluctuations.

Use Cases: Critical Sites That Require Dual SIM

Site	Impact of an Outage	Recommendation
Drinking Water Pumping Station	Interruption in drinking water supply	Dual SIM required
High-Voltage Substation	Loss of control over the power grid	Dual SIM required
Wastewater Treatment Plant	Treatment failure, environmental risk	Dual SIM recommended
Production PLC	Line shutdown, production losses	Dual SIM recommended
Measurement sensor	Data gaps	Multi-carrier M2M SIM sufficient
Commercial building BMS	Loss of monitoring	Multi-carrier M2M SIM sufficient

The Eziwan Approach

The Eziwan Gateway features two M2M SIM slots and automatic failover firmware. The watchdog configuration (test ping, failover thresholds, response timeout) is performed via the Eziwan Cloud without requiring physical access to the gateway.

Learn more: industrial 4G router, multi-carrier M2M SIM, and 4G router with VPN.

Frequently Asked Questions

Industrial 4G RouterEverything You Need to Know About 4G Routers for Field Locations.Learn more Multi-carrier M2M SIMA SIM card that automatically switches carriers.Learn more 4G Router with VPNCombine 4G and VPN in a single device.Learn more Connectivity for Remote SitesConnect without a fixed infrastructure.Learn more Remote Site MonitoringView the network status for each site.Learn more Eziwan GatewayThe Eziwan dual-SIM LTE gateway.Learn more

Why Dual SIM Is Essential at Critical Sites​

Dual-SIM Architecture​

Failover Configuration Criteria​

Use Cases: Critical Sites That Require Dual SIM​

The Eziwan Approach​