"Chiami la sicurezza!"

Translation: Call security!

[die7fox]

Isn't the imperative of chiamare "chiama?"

[marziotta]

Yes, the informal is "Chiama!".

The courtesy form is "Chiami!"

If "Chiama" is not accepted, you should report it. :)

[PM-PM-PM]

Sometimes it helps to look at the verb conjugations for clarity when one gets confused. This web site may help. Look at the Imperativo.
http://www.coniugazione.it/verbo/chiamare.php

[Brian211237]

Why isn't you call security accepted

[roman2095]

Duolingo uses the exclamation mark to indicate the imperative mood. If you remember that you will have a lot fewer answers dinged.

[AdiYan12]

should be accepted

[baggiemews]

The tu and lei forms swap places in "are" imperative. Use the above site to compare the imperative in "are", "ere" and "ire" forms (http://www.coniugazione.it/verbo/chiamare.php)

[keeper.here]

why 'call THE security' not accepted?