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All alarm systems manufactured for use in the UK in ’99 were required to operate on the frequency of 433MHz. Subsequently, in late 2000, the government allowed the introduction of the “Tetra” radio network for telecommunications companies, the military, police, fire and ambulance services etc, which was allocated the 420-430MHz bandwidths.

Although not exactly the same frequency, these “Tetra” transmitters are licensed and so are allowed to operate at around 20,000 watts, compared with the alarm systems 0.5 watt radio key (necessary so that your radio keys remain exempt from annual licensing fees!)

As a result, when you are near a transmitting “Tetra” mast you can get a degree of “bleed over” as their signal is so much stronger and this can swamp the transmission from the radio key.

This problem is not exclusive to this system and can occur on any number of manufacturers systems produced prior to 2001.

The receiver boards were redesigned to focus more accurately on the 433.92HHz frequency as soon as this problem became evident and these are the commonly known as the 'shielded' units. This term is a little misleading as no 'shielding' has been carried out, but simply refers to the later receiver boards in appearance.

Systems manufactured before 2001, with the older receiver boards may experience this problem, but are not faulty and were not considered eligible for warranty at the time.

However, as a goodwill measure, customers who suffered from 'exceptional' radio lock-out (i.e. lived or worked below a mast) were offered an upgraded receiver board whilst the vehicle was still within the warranty period.

This goodwill period was extended for a further 12 months after the 3 year warranty period expired, but ended in December 2004.

Later ECUs with the "Tetra resistant" receiver are still available from Subaru (part number SACC 3465 iro £70)


There are a few points that should be remembered:

  • All vehicles that passed through the import centre from January 2001 are equipped with the latest receiver boards that are "Tetra Resistant" and so should not experience this problem.
  • A keypad is fitted to ALL models with the UK standard fit alarm system (from 99 MY) as an emergency override, in the event of loss, damage, flat radio key battery etc. (The keypad also allows the driver to access a number of features and is a complete programming tool for the dealers) and so pushing/recovery of vehicle’s should not be necessary provided you know your override PIN and ow to operate the keypad.
  • The keypad can NOT be affected by "Radio Lock-Out", as it is hard wired into the system and does not rely on a radio transmission.

Information source - SIDC forum thread Ian aka Sigma Sam - Solves all your OEM Alarm Problems

Page last modified on September 29, 2007, at 10:44 PM
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