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Body wires
TTI
  
CST-581
Covert surveillance transmitter

CST-581 1 is a body-wearable surveillance transmitter, developed in 1991 by Tactical Tech­no­lo­gies, Inc. in Folsom (Pennsylvaina, USA). The device uses narrowband Frequency Modulation (FM), and operates on a single crystal-controlled frequency in the VHF-H band (150-174 MHz).

The device is housed in a black metal enclosure that consists of two case shells. The upper 1/3rd contains the actual transmitter, whilst the lower 2/3rd holds the batteries. At the top is the ON/-OFF switch, as well as sockets for antenna and microphone. A covered hole (marked 1-2) sug­gests that there was also a 2-channel version.

The device shows a remarkable resemblance to transmitters like the TX-916 from competitor LEA-AID. Even the enclosure and the con­struc­tion is nearly identical. It is clear that both com­panies targeted the same potential customers. 		  

This page currently acts as a placeholder for future information about this device. At present, we don't even know the device's correct designator, as the original label is missing. If you have additional information about this device, please contact us.

  1. CST-581 is probably not the correct designator. It is a 'best guess', based on the age of the device, the components used, and information of comparable items in the FCC database.
TTI body-wearable transmitter
Top view
Right angle view
With open battery compartment
Bare transmitter (without batteries)
Battery terminals with serial number and company name
Covert electret microphone
Electret microphone
A
×
A
1 / 8
TTI body-wearable transmitter
A
2 / 8
Top view
A
3 / 8
Right angle view
A
4 / 8
With open battery compartment
A
5 / 8
Bare transmitter (without batteries)
A
6 / 8
Battery terminals with serial number and company name
A
7 / 8
Covert electret microphone
A
8 / 8
Electret microphone
❮ ❯

Interior
The interior of the device can be accessed by removing the nuts from the SMC antenna connector and the 2.5 mm microphone jack socket, after which the metal case shell can be taken off. This reveals the interior as shown in the image below. Inside the device are two printed circuit boards: a smaller and a larger one. The larger one at the bottom, holds the crystal-controlled tran­smitter. The smaller one at the top holds the microphone amplifier and the power circuit. The ed­ges of both PCBs are soldered to the metal frame. The red wire is connected to the power terminals.



Interior with case shell
Interior - right angle view
Interior - left angle view
Interior - seen from the top
Antenna circuit detail
PCB detail - the crystal is just visible
PCB and wiring detail
Two stacked PCBs
B
×
B
1 / 8
Interior with case shell
B
2 / 8
Interior - right angle view
B
3 / 8
Interior - left angle view
B
4 / 8
Interior - seen from the top
B
5 / 8
Antenna circuit detail
B
6 / 8
PCB detail - the crystal is just visible
B
7 / 8
PCB and wiring detail
B
8 / 8
Two stacked PCBs
❮ ❯

Restoration
When we received the device in August 2026, it was in good cosmetic condition. It came with a suitable electret microphone, but the wire antenna (with SMC connector) was missing. A quick test confirmed that the device was working at a spot frequency of 166.500 MHz. No restoration or repair is currently necessary.

Missing
  • Wire antenna for 166.500 MHz with SMC connector
Specifications
  • Device
    Body-wearable surveillance transmitter
  • Purpose
    Covert overhearing of conversations
  • Model
    CST-581 1
  • Manufacturer
    TTI
  • Year
    1991 ~
  • Country
    USA
  • Frequency
    150-174 MHz
  • Channels
    1 2
  • Waveform
    Narrowband FM
  • Oscillator
    Crystal-controlled
  • Output
    1 W
  • Microphone
    Electret (external)
  • Approval
    ?
  • Power
    9 V/DC (2 × wired in parallel)
  • Dimensions
    HWD: 93 × 58 × 20 mm
  • Weight
    104 g (without batteries)
  • Price
    ?
  1. Probably not the correct designator.
  2. The device featured here works at a spot frequency of 166.500 MHz.
Further information
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© Crypto Museum. Created: Sunday 30 August 2026. Last changed: Thursday, 03 September 2026 - 14:18 CET.
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