undetectable
adj. B2 Upper Intermediate US //əndɪˈtɛktəbəɫ// UK //ˌʌndɪtˈɛktəbəl// un·de·tectable
adj. so small or hidden that you cannot see, hear, or find it. You use this to describe things that are completely invisible or impossible to notice.
adj. impossible to perceive, identify, or measure by any known means. Often used to describe very low levels of a substance or a signal that is masked by background noise.
The virus is undetectable in the blood test.
The new software allows the spy to remain undetectable even when the system is actively scanning for malware.
The signal was so weak that it became undetectable by the receiver, making it impossible for the researchers to track the satellite's exact position.