Like all forms of evidence, handheld devices require certain precautions to preserve their value for an investigation. During the collection of cellular phones, there has been a debate on how to best preserve their data. This debate centers on whether to turn the phone off or leave it on at collection. It is recommended to power the phone off to preserve data and battery power. If for some reason this is not possible, then the phone needs to be protected from cell tower signals. There are packaging products created for signal protection, such as the Stronghold Bag™ (Paraben Corporation), or an unlined quart-sized paint can, also known as an arson can. However, leaving a cellular phone powered on in a signal blocking container increases the device’s active search for a cellular network. This increased activity will cause battery failure at a quicker than normal pace. If protective packaging is utilized, then a method of powering the device should be considered, or the examiner should be alerted so that an immediate examination can be conducted.

When the phone is turned off, it can be packaged in a paper evidence bag and sealed with evidence tape. To simplify the forensic examination, handheld devices should be packaged separately from other evidence and, when possible, their charging cords/adapters should be packaged with them. If a pass code is known for the phone by the arresting officer or investigator, it should be written on a piece of paper and packaged with the phone.

From: Examining Cellular Phones and Handheld Devices by Don L. Lewis