The Collaborative International Dictionary of English v.0.48:

Unwatchful \Unwatchful\
   See watchful.

WordNet (r) 3.0 (2006):

unwatchful
    adj 1: not alert to what is potentially dangerous [syn:
           unalert, unwatchful, unvigilant] [ant: alert,
           watchful]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "unwatchful":
   asleep, culpably negligent, derelict, goofing off, inadvertent,
   inattentive, incautious, laissez-faire, lax, loose, napping,
   neglectful, neglecting, negligent, nodding, noninterfering,
   nonrestrictive, off-guard, overly permissive, permissive,
   procrastinating, relaxed, remiss, scamping, skimping, slack,
   sleeping, slighting, slurring, unalert, uncautious, uncircumspect,
   unguarded, unprepared, unready, unrigorous, unvigilant, unwary