It is only in this chapter of Daniel (see also verses 17 and 23) that certain angelic beings called "watchers" are mentioned. Whether the term applies to all God's holy angels or only to a certain order of angels has not been revealed in Scripture.
However, we do know that at least some of the angels, if not all of them, are intensely occupied with observing events among humans here on earth. For example, Paul said that he and the other apostles had been made "a spectacle unto the world, and to angels, and to men" (1 Corinthians 4:9).
The word "spectacle" in this verse is actually "theatre," and is so translated the only other time it is used in the New Testament (Acts 19:29, 31). It is sobering, as well as surprising, to realize that Christians--especially Christian leaders--are on a stage, as it were, being carefully watched by an audience which even includes the angels.
Paul also cautioned Christian women to maintain a covering on their heads "because of the angels" (1 Corinthians 11:10). Perhaps the watching angels are also included in the great "cloud of witnesses" who observe us as we "run with patience the race that is set before us" (Hebrews 12:1).
But why should these mighty angels, these "holy ones," these heavenly "watchers," have such a "desire to look into" these things here on earth? (1 Peter 1:12). Perhaps they are anxious, like us, to "see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God, who created all things by Jesus Christ: To the intent that now unto the principalities and powers in heavenly places might be known by the church the manifold wisdom of God" (Ephesians 3:9-10). HMM http://www.icr.org/articles/type/6/