A mobile phone seized during an investigation is more than an ordinary electronic device. It may contain messages, photographs, location records, login details, communication histories and information stored in applications. At the same time, it remains an active device capable of communicating with cellular networks, Wi-Fi, Bluetooth and remote services.
Preserving its evidential value therefore involves more than taking the phone and transporting it to a laboratory. Investigators must be able to show who collected it, what condition it was in, who handled it and to whom it was transferred. This documented process is known as chain of custody.
What does chain of custody mean?
Chain of custody records the complete movement of an item from collection through analysis, storage or presentation in legal proceedings. Its purpose is to demonstrate that the item presented is the one originally collected and that no unexplained handling occurred.
Current SWGDE guidance for mobile-device evidence states that documentation should be contemporaneous. It should include a description of the item, unique identifiers, the date and time of receipt or transfer, and the identity of every person taking possession.
For a mobile phone, records will commonly include:
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the manufacturer, model and serial or other identifying number,
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the location and time of collection,
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whether the device was powered on and locked,
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the condition of the display and visible information,
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connected equipment or cables,
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actions performed and settings changed,
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transfers between personnel and facilities.
A custody form does not protect the digital data by itself. Wireless communication must also be addressed.
Why is mobile evidence different?
A traditional physical item does not normally change by itself during transportation. A powered mobile phone, however, can receive messages, synchronise information, update application content or respond to a remote command.
Remote locking or wiping represents one of the most serious risks. Even routine incoming data can be problematic because it changes the state of the phone after collection. It may later be more difficult to determine which information existed at the relevant time and which arrived afterwards.
The NIST Guidelines on Mobile Device Forensics therefore identify radio isolation as one of the available methods for protecting mobile-device evidence.
Where does Faraday isolation fit?
A Faraday bag creates a physical barrier between a device and surrounding wireless networks. A phone can remain powered on while being prevented from communicating normally through cellular networks, Wi-Fi, Bluetooth, GPS, RFID or NFC.
In forensic practice, this reduces the risk of remote intervention, prevents the receipt of new network data and allows the device to be transported without ordinary connectivity.
A Faraday bag does not create the chain of custody on its own. It cannot replace item identification, personnel records, timestamps or documentation of examiner actions. It is a technical safeguard that complements the procedural and administrative controls surrounding the evidence.
Isolation and evidence of physical handling
Two separate questions must be considered. Could the phone communicate wirelessly during transport? Could someone physically access the stored device?
Faraday isolation addresses the first question. A seal or another tamper-evident feature helps address the second. Their combination can be useful when a device moves between the collecting officer, an evidence store and a forensic laboratory.
Two options for different forensic scenarios
The FWR Faraday Bag Small Gen. M is designed for secure storage and transport of mobile devices. It uses a 12-layer shielding construction, magnetic closure and measured attenuation of up to 102 dB. Its magnetic design is particularly practical for repeated handling in a laboratory or in the field and reduces the risk of catching or damaging protective gloves.
Where both RF isolation and evidence of physical access are required, the FWR Faraday Bag Small Gen. M with sealing option adds the ability to apply a seal. During handover, the seal can help show whether the Faraday bag was opened while in transport or storage.
A seal does not establish the origin or content of digital data by itself. Combined with a case number, evidence identifier, timestamps and signatures, however, it supports transparent handling records.
Technology must support the procedure
Evidence integrity is not created by a single product. It results from documentation, accountability, physical security, network isolation and subsequent forensic acquisition working together.
The role of a Faraday bag is specific: it restricts wireless communication during the sensitive period between collection and forensic processing. A sealable version adds a visible control against unrecorded physical access.
Chain of custody is therefore more than a list of signatures. It is a continuous and demonstrable history of the evidence, from the place of collection to the final analysis.
