Also that some devices log data locally and require manual pickup + review to avoid detection. Also LEO have been known to temporarily disable such devices when people do scans to detect them for Undercovers.
Since I'm not seeing any other references, here's a timestamp for a YouTube video where an ex-undercover op is interviewed and such thing is mentioned:
How FBI Undercover Agents Actually Work | Authorized Account | Insider https://youtu.be/h6au3ppTm7g?t=1123
