Only as safe as the device themselves. Which are not safe.
Signal only provides privacy against carriers and internet transport. It will not protect you against three letter agencies or google or apple. Or any invasive keyboard you may have installed or comes factory.
Edit: think of it as a privacy app with superior texting, rather than a security app.
The can snoop but they need a warrant for comms to be admissible as evidence.
And using signal is a red flag for the Enemy to pay more attention to you
(post is archived)