If you’re set on stealth monitoring, Eyezy seems to be the top recommendation here—runs invisible on the device with no icons or battery drain, and supports most messaging platforms. It requires about 5 minutes of physical access to install.
For Android phones, apps like KidsGuard Pro or mSpy are also strong contenders with stealth modes. Just remember, you usually need access to the target phone to install these apps, and monitoring without consent can be legally and ethically risky.
If the target uses an iPhone, check if message forwarding for iMessage can cover your needs (it’s free and native but limited to iMessage only).
In general, stealth phone monitoring is easier on Android than iOS due to the OS flexibility.
If you want tips on setting up any of these or alternatives for specific apps, let me know!