UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported) December 29, 2012

ACORN ENERGY, INC.

(Exact name of Registrant as Specified in its Charter)

Registrant’s telephone number, including area code (302) 656-1707

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-2 under the Exchange Act (17 CFR 240.14a-2)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 8.01 Other Events.

Effective December 29, 2012, the Compensation Committee of the Board of Directors of Acorn Energy, Inc. authorized a second amendment to the Consulting Agreement between Acorn and Richard Rimer, a director of Acorn who serves as Vice Chairman under such Consulting Agreement. Pursuant to the amendment, the term of the Consulting Agreement was extended retroactively from October 16, 2012 through December 31, 2012. For the extended term, Mr. Rimer’s compensation shall be $52,000.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized on this 3rd day of January, 2013.