NEW YORK (Dow Jones/AP) – Shares of LoJack Corp. tumbled Thursday after giving up modest ground all week, prompting one analyst to speculate that some investors are concerned a sharp drop in demand for cars might damp installations of the company’s theft-recovery systems.

Stock of the Westwood, Mass.-based company fell $2.25, or 11 percent, to finish at $18.29 on the Nasdaq Stock Market.

Thursday’s weakest level was $18.17. On a 52-week basis, there was a low of $10 last Sept. 15 and, more recently, a high of $22.70 on Aug. 24.

Needham & Co. analyst Andrew Spinola said Thursday that assuming investors are somewhat concerned about lackluster demand for automobiles, a sell-off of LoJack shares is all the more likely because the stock has performed well for much of the year, particularly since reporting last month that its second-quarter profit more than doubled on strong sales.

Spinola, who carries a “buy” rating on the stock and a $23 price target, contends that concerns about the effect of weak auto sales are overblown because while the dollar amount of sales was lower, unit sales of light vehicles had shown an increase.

LoJack’s systems, which are installed in automobiles, help police track the vehicle in the event that it is stolen.

On Wednesday, the Commerce Department said overall U.S. retail sales showed their sharpest drop in more than three years in August amid a precipitous drop in demand for automobiles. Retail sales decreased a seasonally adjusted 2.1 percent, dragged down by a 12 percent decline in auto dealer sales.

The government’s sales report comes about a month after news of LoJack’s second-quarter performance sent shares up 22 percent to $20.93 in a single day, Aug. 9. And though the shares have retreated from their Aug. 24 high of $22.70, they hadn’t until Thursday dipped below the $20 mark since Aug. 9.

Analyst David Gold, with Sidoti & Co., discounts the notion that sluggish automobile sales would affect LoJack too deeply, noting that the company has improved its market penetration and that a majority of its customers are buyers of foreign cars. Sales of these cars have generally fared better than those produced by Detroit’s Big Three, he noted, which affords LoJack some protection.