Can I Record My Spouse Without Them Knowing It?
In Illinois, such activity would be covered under the eavesdropping law and the eavesdropping laws says that you cannot record somebody surreptitiously, AKA without them knowing about it, except in very limited circumstances.
The most common limited circumstance that you can record somebody without them knowing about it is if there's a reasonable suspicion that they have committed a crime, are committing a crime or about to commit a crime, and that there's reason to believe that evidence of said crime could be obtained by recording the person.
So in general, the answer is no. You can't surreptitiously record your spouse. But if the recording falls under that exemption and you can record without it being a crime.