-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 NQTbAmMD50tCt1A5f1wvmYu7nV2WHqmfSUUVr0VyfTWwBYv17myw5Z7CBwuBgQe5
 otl5s6N6vU8e9gsXMUgBLw==

<SEC-DOCUMENT>0001284743-04-000002.txt : 20040324
<SEC-HEADER>0001284743-04-000002.hdr.sgml : 20040324
<ACCEPTANCE-DATETIME>20040324170812
ACCESSION NUMBER:		0001284743-04-000002
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20040323
FILED AS OF DATE:		20040324

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BEEBER PAUL STEPHEN
		CENTRAL INDEX KEY:			0001284743

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-10004
		FILM NUMBER:		04687865

	MAIL ADDRESS:	
		STREET 1:		333 BAYVIEW AVENUE
		CITY:			AMITYVILLE
		STATE:			NY
		ZIP:			11701

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			NAPCO SECURITY SYSTEMS INC
		CENTRAL INDEX KEY:			0000069633
		STANDARD INDUSTRIAL CLASSIFICATION:	COMMUNICATIONS EQUIPMENT, NEC [3669]
		IRS NUMBER:				112277818
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0630

	BUSINESS ADDRESS:	
		STREET 1:		333 BAYVIEW AVE
		CITY:			AMITYVILLE
		STATE:			NY
		ZIP:			11701
		BUSINESS PHONE:		5168429400

	MAIL ADDRESS:	
		STREET 1:		333 BAYVIEW AVE
		STREET 2:		XXXXXXXXXXXXXXXXXXX
		CITY:			AMITYVILLE
		STATE:			NY
		ZIP:			11701
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-03-23</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000069633</issuerCik>
        <issuerName>NAPCO SECURITY SYSTEMS INC</issuerName>
        <issuerTradingSymbol>nssc</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001284743</rptOwnerCik>
            <rptOwnerName>BEEBER PAUL STEPHEN</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>130 NEWBRIDGE ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>HICKSVILLE</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>11801</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>NAPCO Security Systems Inc.Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-03-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>12.35</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Spouce</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <ownerSignature>
        <signatureName>Paul Stephen Beeber</signatureName>
        <signatureDate>2004-03-24</signatureDate>
    </ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----