-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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<SEC-DOCUMENT>0001285237-05-000004.txt : 20050819
<SEC-HEADER>0001285237-05-000004.hdr.sgml : 20050819
<ACCEPTANCE-DATETIME>20050819160825
ACCESSION NUMBER:		0001285237-05-000004
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050818
FILED AS OF DATE:		20050819
DATE AS OF CHANGE:		20050819

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

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Blaustein Randy B
		CENTRAL INDEX KEY:			0001285237

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-10004
		FILM NUMBER:		051038791

	BUSINESS ADDRESS:	
		STREET 1:		333 BAYVIEW AVENUE
		CITY:			AMITYVILLE
		STATE:			NY
		ZIP:			11701
		BUSINESS PHONE:		6318429400

	MAIL ADDRESS:	
		STREET 1:		333 BAYVIEW AVENUE
		CITY:			AMITYVILLE
		STATE:			NY
		ZIP:			11757

	FORMER NAME:	
		FORMER CONFORMED NAME:	BLAUSKIN RANDY B
		DATE OF NAME CHANGE:	20040330
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-08-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001285237</rptOwnerCik>
            <rptOwnerName>Blaustein Randy B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>333 BAYVIEW AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>AMITYVILLE</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>11757</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</value>
            </securityTitle>
            <transactionDate>
                <value>2005-08-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>9600</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.7188</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>48000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>NAPCO Security Systems, Inc. Employee Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>1.7188</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-08-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>9600</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.7188</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2000-09-27</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2005-09-27</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>NAPCO Security Systems, Inc. Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">An Option to purchase 20,000 shares was issued on 9/27/00 at $4.125 per share. Due to a stock split the number of shares were increased to 40,000 and the exercise price was adjusted to $2.0625. On April 15, 2004, 32,000 shares (post split) were purchased, leaving a balance of 8,000 shares. In November 2004, as a result of a 20% stock dividend the the number of remaining shares were increased to 9,600 and the exercise price was adjusted to $1.71875.</footnote>
        <footnote id="F2">Option to purchase stock is exercisable , cumulatively, at 20% per year commnencing 9/27/00.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Randy B. Blaustein</signatureName>
        <signatureDate>2005-08-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----