Microphone blocker


A microphone blocker is a phone microphone connector used to trick feature phones that have a physical microphone switch to disconnect the microphone. Microphone blockers won't operate on smartphones or laptops because the microphone is controlled with software rather than a physical switch.

Safety test

Hardware devices should always be tested if it is controlled by software which renders a microphone blocker useless. This can simply be done by plugging a headset or a microphone to the jack try to activate the internal microphone, or any program that always will use the internal microphone for other hardware devices like laptops.

Working alternatives for modern hardware devices

Microphone blockers, including commercial microphone blockers with a integrated circuit marketed to provide "extra security", are not useful for smartphones because it is controlled entirely by software. It can be demonstrated by connecting a microphone blocker to a smartphone, and make a phone call with speaker mode which will also active the internal microphone.
However, although they would work, there are further problems:
A phone connector without a microphone channel cannot be used as a microphone blocker because it will not deactivate the external microphone. Three- or four-conductor 2.5 mm and 3.5 mm sockets are common on older cell phones and newer smartphones respectively, providing mono or stereo sound and a microphone input, together with signaling.

Older hardware devices

/AHJ is the de-facto TRRS standard. OMTP was mostly used on older hardware devices. However, the old mobile phones have a 2.5 mm jack connectors socket and cannot be used with modern microphone blockers that are typically 3.5 mm, but old mobile phones are notorious for their low security of the hardware itself. If a CTIA headset is connected to a mobile phone with OMTP interface, the external microphone will stay active. There, internal microphone will only be active when holding the microphone key on the headset. A standard TCIA/AHJ TRRS microphone blocker cannot be used with OMTP socket hardware devices and it is recommended to test all microphone blockers to make sure they really work.

Operation

Microphone blockers disable the internal microphone by tricking the device into believing an external microphone is connected. A 3.5 mm microphone blocker with just channel is enough to disconnect the internal microphone, but most commercial microphone blockers have connections which in theory makes them headset blockers that in smartphones also disconnect the internal speaker in media player software because they will try to connect to the headphones, while ringtones, and alarms, will functioning as normal because they will use both the internal speaker and the external speaker.
Successful operation of a microphone blocker depends on the internal scheme of the mobile device, which may fully block the microphone without possibility of recovering data, or just disregard the signal from internal microphone with the possibility of recording if needed.

Issues

Some devices allow internal and external microphone works simultaneously or may not recognize when an external microphone is connected.

Types

Microphone blocking plug

A microphone blocking plug is a phone connector with a microphone channel that cannot be used due to the plugged end. Some products are shipped with a female connectors to prevent loss when the male connector is detached. A mobile phone charm can be used to conceal a dummy blocker.
A microphone blocking plug can be used to debug software-defined radio that demands a connector to be plugged but they cannot be used to stream radio due to its low antenna efficiency.

Life hack

Common products that can be used as microphone blockers:
It's possible that microphone connectors without a microphone circuit like the above solutions offer low security, because when you plug a connector that has no microphone or microphone circuit, software has the ability to override the default behavior.

Microphone blocking adapter

with an integrated microphone blocker also exist, allowing users to use the headphones without risking being eavesdropped. Microphone blocking adapters are phone connectors adapters with a microphone channel and a mechanism that produces a false positive signal simulating a connected microphone. This mechanism cannot be built by pairing multiple connectors: a headset connected to a 3.5 mm TRRS headset extension cable adapter further connected to a 3.5 TRS headphone cable adapter won't trick a connected mobile phone to disconnect its external microphone.

Applications

This section describes use for both microphone blocking plugs and adapters.

Use

Eavesdropping protection for feature phones

A microphone blocker is a cheap, simple accessory that provides countersurveillance against eavesdropping, for example recording eavesdropping from interception, or phone hacking, but it doesn't work on smartphones because they are controlled by software. However, there are a variety of computing vulnerabilities like proprietary software and firmware, backdoors, hardware security bugs, hardware backdoors, hardware Trojans, spyware, and malware programs that can turn on a mobile device's microphone remotely, and the vast majority of devices do not have internal hardware protection to prevent eavesdropping. Most antivirus software, and anti-spying software does not guarantee that the microphone will be fully blocked or disabled and can even be prevented doing so by spyware and malware that are constantly changing and improving.
Leaked documents published by WikiLeaks, codenamed Vault 7 and dated from 2013 to 2016, described the capabilities of the United States Central Intelligence Agency to perform electronic surveillance and cyber warfare, including the ability to compromise the operating systems of most smartphones, turning them into permanent listening devices. Millions of smartphones could also be vulnerable to software cracking via accelerometers.
A new acoustic cryptanalysis technique discovered by a research team at Israel's Ben-Gurion University Cybersecurity Research Center allows data to be extracted using a computer's speakers and headphones. Forbes published a report stating that researchers found a way to see information being displayed, by using microphone, with 96.5% accuracy.

Pocket dialing protection

A microphone blocker is useful to prevent a mobile phone against audio interception from pocket dialing.

Abuse

Social engineering

A person can wiretap conversations from persons they with social engineering have deceived that microphone blockers are safe to use with smartphones. This can in theory be exploited by companies that manufacture and sell commercial microphone blockers if they require a mobile phone number when people order their products or ask for support.

Marketing ethic issue

Manufacturers of commercial microphone blockers with 3.5 mm phone jacks intended for smartphones, sometimes claim that they their blocker has an inbuilt semiconductor integrated circuit that will offer superior security but doesn't give any security at all, they just deceive people to make money on them. This has raised questions about marketing ethics.