My wife saw this on a sign in a high-school attendance office.

Problem:
The adjective is a bastardization of two perfectly good ones.

Explanation:
The sign directed visitors in the office to turn off such devices.

While “electronical” does appear in the Unword Dictionary and the Urban Dictionary on the Web, those dictionaries are not representing that this a proper adjective.

Search www.dictionary.com, in contrast, and you won’t find a match for this nonsense word.

I believe that the sign writer wanted sign readers to turn off cell phones, pagers, etc., and that the sign writer believed at least one of the following:

• that “electronical” sounded more intelligent than “electrical” or “electronic”;
• that “electronical” must be correct because it’s so close to “electrical” and “electronic”;
• that “electronical” must be correct because “electronically” is a valid adverb.

What is disheartening is that a Google search for “electronical” (with the quotation marks) returned about 1,090,000 matches. Fortunately, a search for “electronic” (with the quotation marks) returned about 526,000,000 matches, and a search for “electrical” (with the quotation marks) returned 221,000,000 matches.

We get the solution by reviewing the definitions of “electrical” and “electronic”:

• “electrical” — related to or operated by electricity
• “electronic” — of or related to electronics, where “electronics” today usually refers to the science dealing with the flow of electrons in semiconductors (e.g., in cell phones)

Solution:
“Electronic Devices”