Short answer
A slave field lock reaches its master over Bluetooth at close range or LoRa up to 1 km in open area, and carries no cellular radio and no GPS of its own. It borrows both from the master. That removal is what buys up to three years of standby, and it costs the lock its independence.
Key takeaways
- The JT709ex link to its master is Bluetooth or LoRa, with LoRa reaching up to 1 km in open area, not a cellular link at all.
- It has no cellular radio and no GPS: both come from the paired JT701 master, which is the only device on the cellular network.
- Removing those two radios is what makes up to 3 years of standby possible; the JT701 keeps 15,000 mAh because it never sleeps.
- Range is the wrong single question, Bluetooth and LoRa answer two different distances, and the yard layout decides which one carries the traffic.
- What the design trades away is independence: out of link range, the field lock still locks, but nothing reaches the platform.
01What the two link options actually are
The specification row that matters here is short: the link from the JT709ex field lock to its JT701 master is listed as Bluetooth or LoRa, and the LoRa figure is up to 1 km in open area. Neither is a cellular technology, and that is the point. Bluetooth is a short-range radio designed for devices within a few metres of each other, which fits the case where the master sits on the tractor cab and the field lock sits on a valve on the same trailer. LoRa is a long-range, low-rate radio designed to carry very small messages across a wide area on very little power. So the pair is not choosing between a fast link and a slow one. It is choosing between a link that assumes the two devices are almost touching and a link that assumes they may be at opposite ends of a depot.
02Why 1 km is a ceiling, not a promise
The published LoRa figure carries a qualifier that is easy to skip: up to 1 km in open area. Both halves of that qualifier do work. "Up to" means the number is the best case under favourable conditions rather than a distance the link will hold everywhere. "Open area" means the measurement assumes nothing substantial sits between the two radios. A fuel depot is not an open area. Steel tank walls, parked tankers, concrete blast walls and loading gantries all absorb or reflect radio energy, and a link that reaches a kilometre across empty desert may reach a fraction of that between two rows of tanks. The practical reading is to treat 1 km as an upper bound for planning, then verify the actual link on the actual site, not to assume the number transfers from the datasheet to the yard.
03What the field lock does not have, and why
Two rows on the JT709ex specification read as absences. Cellular is listed as none, via master. GPS is listed as none, uses master GPS. Read as a feature list, that looks like a device stripped to hit a price. Read as an engineering decision, it is the opposite. A cellular modem is one of the largest consumers in a battery-powered device, because registering on a network, holding a session and retransmitting through weak coverage all cost energy on a schedule the device cannot control. A GNSS receiver is the other large consumer, since acquiring a fix means listening to faint satellite signals for a sustained period. Take both out and what remains is a lock whose radio work is a short exchange with a master that is already awake and already connected.
04The number that removal buys
The two devices make the trade visible when their power rows are placed side by side. The JT709ex is listed with ultra-low power consumption and a standby life of up to 3 years. The JT701 is listed with a 15,000 mAh lithium-ion cell. The larger battery belongs to the device with the shorter expected interval between charges, which looks backwards until the radios are accounted for. The JT701 carries GSM and 3G on dual SIM plus a built-in GPS receiver quoted at 2.5 m CEP, and all three are working while the vehicle moves. The JT709ex carries none of them. So the useful generalisation is that a standby figure is mostly a statement about which radios are present and how often they wake, and only secondarily a statement about cell capacity.
05What the link carries, and what it does not
The traffic on this link is small and event-shaped. The field lock publishes alert types for tamper, mechanical key used and shackle cut, and its remote unlock is listed as being performed through the JT701 master on the platform. So the messages travelling over Bluetooth or LoRa are short statements, a lock opened, a shackle cut, a key used, and short commands in the other direction. That is exactly the traffic profile LoRa was designed to carry, and exactly why a low-rate radio is not a limitation here. What the link cannot carry is a position. Since the field lock has no GNSS receiver, the location attached to any of its events is the master's location at that moment, which is a different claim from the lock's own position.
06Where the design stops working
Every borrowed capability introduces a dependency, and it is worth naming this one plainly. If the master is out of Bluetooth and LoRa range, or its own battery is flat, or it is on a stretch of road neither SIM can reach, the field lock is not reporting. It still holds the valve closed, and it still accepts a local Bluetooth or RFID unlock, and its mechanical key still works in an emergency. But no alert leaves the trailer during that window, and the events it recorded reach the platform only once the link is restored. That is a tolerable failure for a sealed compartment on a monitored route and an intolerable one for a lock that must be independently reachable, and the choice between the two is a question about the operation, not about the hardware.
07How to plan the link on a real site
The sequence is short. Decide first where the master will physically live, because every field lock's reachability is measured from that point rather than from the gate or the office. Then measure the real distances to each lock position and compare them against the two link options rather than against the headline kilometre: a valve on the same trailer is a Bluetooth case, a lock across a yard is a LoRa case. Walk the path between them and note what is in the way, since steel and concrete are what turn an open-area figure into a site figure. Confirm the master has coverage on at least one of its two SIMs where the trailer parks, because a working local link into a master with no cellular service still delivers nothing. And decide in advance what the operation will do during a link gap, since that decision is the one the specification cannot make.
| Capability | JT701 (master) | JT709ex (field lock) |
|---|---|---|
| System role | Master (controller) | Slave (field lock) |
| Cellular | GSM / 3G, dual SIM | None, via master |
| GPS | Built-in, 2.5 m CEP | None, uses master GPS |
| Link to the other device | Bluetooth / LoRa | Bluetooth / LoRa, up to 1 km open area |
| Power specification | 15,000 mAh Li-ion | Ultra-low consumption, up to 3 years standby |
| Reaches the platform | Directly | Only through the master |
Figures and sources
- 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 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 quoted standby life: up to 3 years (Source: ENTEK.AI product specification, Jointech JT709ex, 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)
- Jointech JT701 cellular connectivity: GSM / 3G, dual SIM (Source: ENTEK.AI product specification, Jointech JT701, as of 2026-08-31)
- Jointech JT701 quoted GPS accuracy: 2.5 m CEP (Source: ENTEK.AI product specification, Jointech JT701, as of 2026-08-31)
- Jointech JT701 battery capacity, carried because its radios stay on: 15,000 mAh Li-ion (Source: ENTEK.AI product specification, Jointech JT701, as of 2026-08-31)
- Jointech JT709ex alert types carried over the master link: tamper, mechanical key used, shackle cut (Source: ENTEK.AI product specification, Jointech JT709ex, as of 2026-08-31)
Questions
Does the field lock need its own SIM card?
No. Its cellular row is listed as none, via master, so every message it sends travels over Bluetooth or LoRa to the paired JT701, which is the only device in the pair on a cellular network. One subscription serves the pair.
Will the LoRa link really reach one kilometre?
The published figure is up to 1 km in open area, and both qualifiers matter. It is a best case with nothing substantial between the two radios. Tank walls, parked tankers and gantries all reduce it, so treat the kilometre as a planning ceiling and verify the link on the actual site.
Where does a field-lock event get its location from?
From the master. The field lock has no GNSS receiver of its own, so the coordinates attached to a tamper or shackle-cut event are the JT701's position at that moment. For a lock on the same trailer that is usually close enough, but it is a different claim from the lock's own position.
What happens if the master goes out of range?
The field lock keeps holding and still accepts a local Bluetooth or RFID unlock, plus its emergency mechanical key. What stops is reporting: no alert leaves the trailer until the link is restored. Decide in advance how the operation handles that window.