LockCar IS357 intelligent immobiliser review, the micro device that combines tag, app and relay break

The LockCar IS357 is an intelligent micro immobiliser combining a hardwired relay break, wireless tag ID authentication, and mobile app control in a single compact device. It is one of the smallest and most discreet security devices in the LockCar range, and it works on any vehicle from a bicycle to a 24V commercial truck. This review covers its specification, ideal applications, and comparison with the IC3ST.

IS357 technical specification and design

The IS357 is classified as an intelligent micro device because of its compact form factor and the integration of three functions within a single small housing. The relay break function uses the same principle as all LockCar immobilisers: a physical relay in the start circuit that requires authenticated signals to close. The wireless tag ID uses short-range radio communication to detect the presence of the paired tag. The mobile app provides remote status monitoring and backup authentication.

The micro form factor is a significant advantage in installations where space is constrained. The IS357 can be fitted in locations where larger units would not fit, and its small physical footprint reduces the possibility of detection during a casual inspection of the vehicle interior. For owners who place a high value on installation invisibility, the IS357 provides maximum discretion.

12V and 24V support makes the IS357 applicable to the same broad range of vehicles as the IC3ST, including cars, vans, pickups, motorcycles, motorhomes, agricultural vehicles, and specialist transport. The combination of its small size and wide voltage range makes it one of LockCar’s most versatile products.

IS357 compared to the IC3ST

Both the IS357 and IC3ST are standalone dual-factor immobilisers that require no separate MCU. The primary difference is form factor and authentication method detail. The IC3ST uses a 2.4GHz encrypted proximity tag with AES-128 encryption communicating over a dedicated channel. The IS357 uses a wireless tag ID system with mobile app integration. Both provide two-factor protection; the specific technical implementation differs.

The IS357 may be preferred by owners who use their smartphone as the primary control interface and want the tag ID as a seamless secondary factor rather than the primary hands-free authenticator. The IC3ST’s hands-free approach, where the tag automatically disarms on approach, is the most transparent daily-use experience. The IS357 suits owners who prefer slightly more active control over the disarm process.

How LockCar stops this threat

LockCar installs a hardwired relay break in the vehicle start circuit. This break is positioned downstream of the factory immobiliser, the OBD port, and the CAN bus. Even after a successful relay attack or CAN bus injection, the engine will not start because the LockCar relay is open. Closing it requires a second, independent encrypted authentication that relay equipment cannot replicate. LockCar is designed and manufactured in the United Kingdom and installed by mobile engineers at your location.

LockCar recommended products

Top recommendation

LockCar IS357, £149

Primary recommendation for this vehicle type

UK-manufactured and professionally fitted. Mobile installation UK-wide from £150 fully fitted. Full installation documentation provided for insurance purposes.

LockCar IC3ST, £139

Standalone, AES-128 tag, hands-free

The IC3ST sibling with AES-128 encrypted proximity tag hands-free operation. For owners who prefer a fully hands-free experience where the tag disarms automatically on approach.

LockCar One Plus, £259

4G GPS, camera, remote immobilise, combined

Step up to 4G GPS tracking and live camera alongside the relay break. For owners who want both the physical prevention of the IS357 and remote visibility via the LockCar app.