unattended
adj.describing something that is left alone without anyone watching or taking care of it.
adj.not being accompanied, supervised, or cared for by a responsible person. Often used in public safety contexts to describe luggage or vehicles left in a restricted area.
“Do not leave your bags unattended at the airport.”
“The fire started because a candle was left unattended in the living room while the family was outside.”
“Security protocols mandate that any unattended package discovered within the terminal must be reported immediately to the local authorities for inspection and potential disposal.”
Typically used predicatively after 'leave' or 'remain', or attributively before a noun.
When expressing who is not watching the object, use the preposition 'by' rather than 'from'.
“Some businesses even placed radios beside unattended phones, letting local broadcasts fill the dead air while customers waited.”
From un- + attended.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.