Police are carrying out searches in the Oeghill Hill Park area of Lettershandoney outside Londonderry following reports "a device" has been left in the area.
The alert was raised shortly after 10pm on Sunday evening.
The PSNI said it has carried out "extensive searches" but hasn't found anything. No roads have been closed as yet.
A spokeswoman appealed for the public "to be vigilant" and if anyone sees "anything suspicious in the area not to touch it or pick it up" but to immediately call 999.
Police had originally said the device had been left in the area of Drumahoe. Lettershandoney is around three miles outside Derry.
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know.