Generally, there are two accepted collection methods for smartphones, both of which can have pros and cons. Knowing each method, you can decide which is most appropriate given the circumstances of your investigation.

The first collection method is to always turn off the phone upon collecting it as evidence.

The second is to leave the phone off if it is off and leave it turned on if it is on. (Use Faraday protection if you collect a phone that is powered on.)

Faraday bags are fallible, and a device inside the Faraday bag may receive signals from the surrounding mobile network. NOTE: If a charger is attached to a phone inside a Faraday bag, the charger cable may act as an antenna and can allow the phone to receive incoming data.