<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>104 - Disclosure - INVENTORY</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

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</LabelSeparator><Level>2</Level><ElementName>us-gaap_InventoryDisclosureTextBlock</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>terseLabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="from-2012-10-01-to-2013-06-30.1650.0.0.0.0.0.0.0" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;!--DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" --&gt;&lt;div&gt; &lt;div&gt;&lt;!--StartFragment--&gt; &lt;p style="FONT: 10pt Times New Roman, Times, Serif; MARGIN: 0pt 0px"&gt; &lt;strong&gt;NOTE 4- INVENTORY&lt;/strong&gt;&lt;/p&gt; &lt;p style="FONT: 10pt Times New Roman, Times, Serif; MARGIN: 0pt 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;p style="FONT: 10pt Times New Roman, Times, Serif; MARGIN: 0pt 0px"&gt; The components of inventory as of June 30, 2013 and September 30, 2012 were as follows:&lt;/p&gt; &lt;p style="FONT: 10pt Times New Roman, Times, Serif; MARGIN: 0pt 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;table style="BORDER-COLLAPSE: collapse; FONT: 10pt Times New Roman, Times, Serif; WIDTH: 60%" cellspacing="0" cellpadding="0"&gt; &lt;tr style="VERTICAL-ALIGN: bottom"&gt; &lt;td nowrap="nowrap"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 1pt" nowrap="nowrap"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="BORDER-BOTTOM: black 1pt solid; TEXT-ALIGN: center" colspan="2" nowrap="nowrap"&gt;June 30,&lt;br /&gt; 2013&lt;br /&gt; (Unaudited)&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 1pt" nowrap="nowrap"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 1pt" nowrap="nowrap"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="VERTICAL-ALIGN: top; BORDER-BOTTOM: black 1pt solid; TEXT-ALIGN: center" colspan="2" nowrap="nowrap"&gt;September 30,&lt;br /&gt; 2012&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 1pt" nowrap="nowrap"&gt;&amp;nbsp;&lt;/td&gt; &lt;/tr&gt; &lt;tr style="VERTICAL-ALIGN: bottom; BACKGROUND-COLOR: rgb(204,255,204)"&gt; &lt;td style="TEXT-ALIGN: left; WIDTH: 64%"&gt;Parts, materials and assemblies&lt;/td&gt; &lt;td style="WIDTH: 1%"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="TEXT-ALIGN: left; WIDTH: 1%"&gt;$&lt;/td&gt; &lt;td style="TEXT-ALIGN: right; WIDTH: 15%"&gt;296,684&lt;/td&gt; &lt;td style="TEXT-ALIGN: left; WIDTH: 1%"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="WIDTH: 1%"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="TEXT-ALIGN: left; WIDTH: 1%"&gt;$&lt;/td&gt; &lt;td style="TEXT-ALIGN: right; WIDTH: 15%"&gt;229,667&lt;/td&gt; &lt;td style="TEXT-ALIGN: left; WIDTH: 1%"&gt;&amp;nbsp;&lt;/td&gt; &lt;/tr&gt; &lt;tr style="VERTICAL-ALIGN: bottom; BACKGROUND-COLOR: white"&gt; &lt;td style="PADDING-BOTTOM: 1pt"&gt;Work in-process&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 1pt"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="BORDER-BOTTOM: black 1pt solid; TEXT-ALIGN: left"&gt; &amp;nbsp;&lt;/td&gt; &lt;td style="BORDER-BOTTOM: black 1pt solid; TEXT-ALIGN: right"&gt; 62,048&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 1pt; TEXT-ALIGN: left"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 1pt"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="BORDER-BOTTOM: black 1pt solid; TEXT-ALIGN: left"&gt; &amp;nbsp;&lt;/td&gt; &lt;td style="BORDER-BOTTOM: black 1pt solid; TEXT-ALIGN: right"&gt; 78,323&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 1pt; TEXT-ALIGN: left"&gt;&amp;nbsp;&lt;/td&gt; &lt;/tr&gt; &lt;tr style="VERTICAL-ALIGN: bottom; BACKGROUND-COLOR: rgb(204,255,204)"&gt; &lt;td style="PADDING-BOTTOM: 2.5pt; TEXT-ALIGN: left"&gt;Total Inventory&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 2.5pt"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="BORDER-BOTTOM: black 2.5pt double; TEXT-ALIGN: left"&gt; $&lt;/td&gt; &lt;td style="BORDER-BOTTOM: black 2.5pt double; TEXT-ALIGN: right"&gt; 358,732&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 2.5pt; TEXT-ALIGN: left"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 2.5pt"&gt;&amp;nbsp;&lt;/td&gt; &lt;td style="BORDER-BOTTOM: black 2.5pt double; TEXT-ALIGN: left"&gt; $&lt;/td&gt; &lt;td style="BORDER-BOTTOM: black 2.5pt double; TEXT-ALIGN: right"&gt; 307,990&lt;/td&gt; &lt;td style="PADDING-BOTTOM: 2.5pt; TEXT-ALIGN: left"&gt;&amp;nbsp;&lt;/td&gt; &lt;/tr&gt; &lt;/table&gt; &lt;p style="FONT: 10pt Times New Roman, Times, Serif; MARGIN: 0pt 0px"&gt; &amp;nbsp;&lt;/p&gt; &lt;!-- Field: Page; Sequence: 10; Value: 2 --&gt; &lt;!--EndFragment--&gt;&lt;/div&gt; &lt;/div&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>The entire disclosure for inventory. This may include, but is not limited to, the basis of stating inventory, the method of determining inventory cost, the major classes of inventory, and the nature of the cost elements included in inventory. If inventory is stated above cost, accrued net losses on firm purchase commitments for inventory and losses resulting from valuing inventory at the lower-of-cost-or-market may also be included. For LIFO inventory, may disclose the amount and basis for determining the excess of replacement or current cost over stated LIFO value and the effects of a LIFO quantities liquidation that impacts net income.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 210

 -SubTopic 10

 -Section 50

 -Paragraph 1

 -URI http://asc.fasb.org/extlink&amp;oid=6361739&amp;loc=d3e7789-107766



Reference 2: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 210

 -SubTopic 10

 -Section S99

 -Paragraph 1

 -Subparagraph (SX 210.5-02.6)

 -URI http://asc.fasb.org/extlink&amp;oid=6877327&amp;loc=d3e13212-122682



Reference 3: http://www.xbrl.org/2003/role/presentationRef

 -Publisher SEC

 -Name Regulation S-X (SX)

 -Number 210

 -Section 02

 -Paragraph 6

 -Subparagraph a, b, c

 -Article 5



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