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REI
  
ACS-2
Telephone scrambler

ACS-2 is a digitally controlled analogue voice scrambler for regular telephone sets, developed in the early 1990s by Research Electronics Inc. (REI) in Algood (Tenesee, USA). The portable unit was intended for use in combination with the handset of a regular (analogue) desktop telephone set.

The device roughly measures 19.5 x 6.5 x 6 cm and weights approx. 250 grams. It resembles the handset of an old regular telephone set, with a microphone at the bottom, a speaker at the top, and 6 push-buttons and 4 indicators inbetween.

The ACS-2 is powered by a single 9V battery that is installed at the rear, and offers 58,488 code settings, divided over 4 factory controlled banks. To set up a connection, one needs two ACS-2 devices from the same bank (marked A, B, C or D respectively) and set the DIP switches in the battery compartment to the same positions.
  
ACS-2 front side

The ACS-2 was available from REI in 1994 for US$ 249 each [1]. Needless to say that the device hardly offers any protection against eavesdropping whatsoever, as voice scramblers are inherently insecure, and the ACS-2 belongs to the least secure class of such voice scramblers. The product was discontinued by REI many years ago, but surprisingly it is still available from a number of spy shops around the world today (2018), such as the P.S.S. Spy Shop in Amsterdam (Netherlands) [2].

A pair of matched REI ACS-2 phone scramblers ACS-2 front side ACS-2 rear side ACS-2 attached to the handset of a regular phone Regular telephone handset with ACS-2 scrambler Operating instructions Model and serial number tag Battery compartment with code setting (DIP switches)
A
×
A
1 / 8
A pair of matched REI ACS-2 phone scramblers
A
2 / 8
ACS-2 front side
A
3 / 8
ACS-2 rear side
A
4 / 8
ACS-2 attached to the handset of a regular phone
A
5 / 8
Regular telephone handset with ACS-2 scrambler
A
6 / 8
Operating instructions
A
7 / 8
Model and serial number tag
A
8 / 8
Battery compartment with code setting (DIP switches)

Features
The ACS-2 is designed in such a way that it can be fitted to virtually any type of regular telephone handset. At the rear side are a speaker and microphone – both of which are pivoting – that should mate with the microphone and speaker of the telephone's handset. The pivoting feature of the elements at the rear ensures that no ambient sound leaks into the microphone of the handset, whilst an elastic strap is used to keep the ACS-2 tied to the handset during a conversation.


Although the ACS-2 does exactly what was advertised — it is a single frequency sound inverter — it gives its users a false sense of security. The fact that nearly 60,000 different codes can be selected, does not make it any more secure, as it only affects the code that 'opens' the device at the other end, whilst the speech scrambler itself and the inversion frequency remain unaffected. An eavesdropper only has to find the inversion frequency to be able to overhear the conversation.

ACS-2 front side ACS-2 rear side Elastic strap fitted in place ACS-2 attached to the handset of a regular phone Regular telephone handset with ACS-2 scrambler Control panel Indicators Battery compartment with code setting (DIP switches)
B
×
B
1 / 8
ACS-2 front side
B
2 / 8
ACS-2 rear side
B
3 / 8
Elastic strap fitted in place
B
4 / 8
ACS-2 attached to the handset of a regular phone
B
5 / 8
Regular telephone handset with ACS-2 scrambler
B
6 / 8
Control panel
B
7 / 8
Indicators
B
8 / 8
Battery compartment with code setting (DIP switches)

References
  1. Popular Mechanics, Who is listening to your private calls?
    December 1994. Retrieved March 2018.

  2. P.S.S. Spyshop Amsterdam, Anti-bugging systems for telephones ACS-2
    Retrieved March 2018.
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Crypto Museum. Created: Tuesday 20 March 2018. Last changed: Tuesday, 20 March 2018 - 17:52 CET.
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