One SIM, Many Locks: What the Master and Slave Split Actually Changes

Short answer

A master lock holds the cellular link and the GPS receiver; the slave field locks hold neither and are unlocked remotely through it. The consequence is commercial rather than technical: one cellular SIM serves every lock on the vehicle, so SIM and data costs scale with vehicles instead of compartments.

Key takeaways

• The JT701 is listed as master (controller) and the JT709ex as slave (field lock), the roles are published specifications, not configuration choices.
• Only the master carries GSM / 3G on dual SIM and a built-in GPS at 2.5 m CEP; the slave has neither and borrows both.
• The master's specification includes remote slave control: unlock JT709ex remotely via platform, so a dispatcher never needs a second SIM card per door.
• SIM and data cost therefore scales with the number of vehicles rather than the number of compartments, which is the whole point on a multi-compartment tanker.
• The concentration is also the risk: one master is a single point of failure for every lock paired to it.

01The two roles, as the specification states them

The split is not something an integrator configures. It is printed in both product records. The JT701 lists its system role as master (controller). The JT709ex lists its system role as slave (field lock). Those two rows determine everything else on the pair's specification sheets. The master carries GSM and 3G connectivity on dual SIM and a built-in GPS receiver quoted at 2.5 m CEP. The slave carries no cellular radio, its row reads none, via master, and no GPS receiver, its row reading none, uses master GPS. So the pair is not two similar devices, one of which happens to be in charge. It is one connected device and one deliberately unconnected device, designed as a set.

02What the master does on behalf of the others

The master's specification carries a row that makes the architecture concrete: remote slave control, described as unlock JT709ex remotely via platform. That single row is the whole mechanism. A dispatcher issues one command in the platform, it reaches the master over its cellular link, and the master relays it to the paired field lock over Bluetooth or LoRa, a link published as reaching up to 1 km in open area. Events travel the same route in reverse. The field lock's own alert types, tamper, mechanical key used and shackle cut, are generated at the lock and delivered to the platform by the master. The master is therefore acting as both the gateway and the location source for every lock paired to it.

03Why this is a cost question, not a wiring question

Consider a tanker with several sealed compartments, each needing a lock that reports. If every lock carried its own cellular radio, every lock would need its own SIM, its own data plan and its own charging routine. The cost of monitoring the vehicle would then scale with the number of compartments. Under the master and slave split it does not. One master holds the single cellular subscription and the single GPS receiver, and every field lock paired to it rides that connection. Adding a fourth compartment adds a lock, not another SIM card, so the connectivity cost per compartment drops after the first. The platform fee is a separate line: ENTEK.AI prices Smart Lock per device, at 83 SAR per device per month, so ask how paired locks are counted when you compare quotes. That change in shape is what makes the split worth understanding as a purchasing decision rather than a diagram.

04The power consequence of the same decision

The commercial saving and a large operational saving come from the same removal. Because the field lock has no cellular modem and no GNSS receiver, its power rows read ultra-low consumption and a standby life of up to 3 years. The master, carrying both radios, is the device with the 15,000 mAh lithium-ion cell and the charge port. So the architecture does not merely save SIM cards; it also concentrates the charging burden onto one device per vehicle instead of one per compartment. For a depot that has to keep dozens of tankers moving, the difference between charging one device per vehicle and charging four is a real change in maintenance labour, quite separate from the connectivity bill. It also removes three chances per vehicle for a lock to be found flat at the moment it was needed.

05What concentrating everything on one device costs

Every consolidation creates a single point of failure, and it is worth stating this one plainly rather than discovering it on a route. If the master's battery is flat, or it has no coverage on either SIM, or a field lock is parked beyond the link range, then that field lock reports nothing. It still holds. It still opens locally by Bluetooth, RFID or its emergency mechanical key. But its events wait, and the platform sees silence rather than an alarm, which is the failure mode most likely to be misread, because silence looks identical to nothing happening. A design that puts four compartments behind one gateway needs an explicit answer to what the operation does when that gateway is unavailable.

06What the location on a slave event actually means

A second subtlety follows from the borrowing. Since the field lock has no receiver, any position attached to one of its events is the master's position at that timestamp, read from a receiver quoted at 2.5 m CEP. On a single trailer that is close enough for most purposes: the master and the field lock are metres apart. But the two claims are not identical, and the difference becomes material where a master is serving locks that are genuinely separated, a LoRa link stretching toward its published open-area ceiling of 1 km puts real distance between the reported coordinate and the lock. Anyone building a chain-of-custody record from these events should know which device the coordinate came from, because that is the difference between where the asset was and where its gateway was.

07Specifying a pair for a real vehicle

The planning sequence is short. Count the compartments that need to be sealed and reported, and treat that as the number of field locks. Then specify exactly one master per vehicle, and place it where it has the best chance of coverage rather than where it is most convenient to mount. Measure the distance from that mounting point to each field lock and compare it against the two link options rather than against the headline kilometre, remembering that steel and concrete shorten it. Confirm the master has service on at least one of its two SIMs along the whole route, since the entire vehicle's reporting depends on that. Decide in advance what happens during a gateway outage. And keep one charging routine per vehicle for the master, since the field locks are the part of the system you are genuinely allowed to forget.

Figures and sources

• Jointech JT701 system role in the pair: master (controller) (Source: ENTEK.AI product catalogue, as of 2026-08-31)
• Jointech JT709ex system role in the pair: slave (field lock) (Source: ENTEK.AI product catalogue, as of 2026-08-31)
• What the JT701 remote slave control row states: unlock JT709ex remotely via platform (Source: ENTEK.AI product catalogue, as of 2026-08-31)
• Jointech JT701 cellular connectivity, the single subscription the pair shares: GSM / 3G, dual SIM (Source: ENTEK.AI product specification, Jointech JT701, as of 2026-08-31)
• Jointech JT701 quoted GPS accuracy, the position every slave event borrows: 2.5 m CEP (Source: ENTEK.AI product specification, Jointech JT701, as of 2026-08-31)
• Jointech JT709ex own positioning and cellular capability: none, uses the master for both (Source: ENTEK.AI product specification, Jointech JT709ex, as of 2026-08-31)
• Jointech JT709ex link to its master, and range: Bluetooth / LoRa, up to 1 km (open area) (Source: ENTEK.AI product specification, Jointech JT709ex, as of 2026-08-31)
• Jointech JT709ex quoted standby life against the JT701 battery it does not need: up to 3 years, versus a 15,000 mAh cell on the master (Source: ENTEK.AI product specification, Jointech JT709ex, as of 2026-08-31)

Questions

Sources

• ENTEK.AI product specification, Jointech JT701
• ENTEK.AI product specification, Jointech JT709ex

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