Why Faraday Isolation Matters for Chain of Custody
An unshielded seized device can receive a remote wipe in seconds. Faraday bags are now the baseline expectation for protecting digital evidence between seizure and lab examination.
Quick Answer
A Faraday bag isolates a seized device from cellular, Wi-Fi, Bluetooth and GNSS signals so its state cannot be altered between seizure and forensic examination — directly supporting ACPO Principle 1.
The Threat: Remote Wipe and OTA Contamination
Modern smartphones can be wiped, locked or have evidence overwritten by a remote command, an automatic OS update, or even a routine push notification. Once a device is in custody but unshielded, the integrity of every byte on it is at risk.
ACPO Principles 1 and 3 in Practice
ACPO Principle 1 requires that no action change data on a device or storage media. Principle 3 requires an audit trail of all processes applied. Sealing the device into a logged, tamper-evident Faraday bag at the point of seizure satisfies both.
Sealing, Logging and Tamper Evidence
Bags should be tamper-evident, individually serial-numbered, and logged into the case file at the moment of sealing. The seal number, time, location, seizing officer and case reference belong on the exhibit label and in the property log.
What Defence Experts Look For
At trial, the defence will ask whether the device was network-isolated continuously from seizure to examination. Gaps in that chain — including the walk from scene to vehicle to custody — are where cases are lost.
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