The Daewoo Cielo/Nexia had central locking system without a radio remote control.
Central locking
The two rear doors and the front passenger door
had electric motor-driven rack-and-pinion actuators (not mere solenoids) on their doorlock rods.
Each actuator consisted of an electric motor turning a pinion that wound up or down a rack, locking or unlocking its own door alone.
The driver's door had no motor-driven rack-and-pinion actuator -- only a simple SPDT (single-pole-double-throw) switch to activate or reverse the other three doorlock motors.
Remote locking
To enhance this set-up to remote locking, you had to add a motorized rack and pinion actuator for the driver's doorlock rod too.
This actuator would be energized by power-transistors driven by the radio receiver circuit.
Aftermarket suppliers like Autocop provided
- the radio transmitter
- receiving circuit plus
- this additional actuator for the driver's door.
By radio-controlling the driver's door rack-n-pinion actuator, you could lock/unlock all passenger cabin doors.
Hope this clarifies the difference between central locking and remote locking.
Postscript
Inspired by Daimler-Benz’s “Keyless Go” product on the 2000 Mercedes S-class, I had wired my Daewoo Nexia with a Philips "Mifare" contactless SmartCard reader instead of the Autocop analog radio circuits. With the Schlumberger contactless smart-cards, I could separately unlock the passenger cabin and the trunk of my Nexia. Being able to remotely pop-open the trunk was a great convenience.
The idea was to have a contactless SmartCard peripheral interfaced to an in-car embedded computer to automatically secure the car. Back in 2000, my prototype could autonomously wind-up and wind-down the windows and control the central locking system of my new 2000 model Daewoo Nexia.
My current Baleno VXi has a mechanical cable-release for the trunk, instead of the Cielo/Nexia's electric release, so it's a little more complex to remotely unlock the trunk.
Ram
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Off topic:
I used a Philips MiFare ISO 14443A contactless SmartCard peripheral. It fit beautifully into an autorickshaw taillamp lens which I used as the casing. The assembly was fixed on the rear parcel shelf, flush with the rear quarter window.
The main Atmel microcontroller based motherboard was mounted in a polypropylene bread-box in the trunk.
A Schlumberger contactless smart-card presented within five inches of the rear quarter window from outside, unlocked the car and disabled the ignition immobilizer. My carputer also recorded timestamps of when the car was last used. Had to replace the driver's doorlock inside lever, with a motorized one from Autocop.
Used another Schlumberger contactless smart-card with a different digital signature-id to unlock the Nexia's trunk.
The system would also automatically windup the windows and lock the car, if the car was left unsecured for some (programmable amount of) time. One early issue that bugged me, was that after 8-hours in the hot sun, the car's battery voltage would drop below the design 11.5 V.
In summary, it was a hugely successful project, but SmartCard peripheral costs in 2000-2001 prevented me from making it a viable commercial product for India.