It's simpler than you think - one transistor and one "AA" battery. Check it out here.qs
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Actually, it is possible. See this website. I have built this circuit and can verify that it does work, but I had much better success using 2N2222 transistors. Also, you need around 12 volts for it to work properly. Hope this helps!
You'll need a little more than a transistor. You need some kind of timer (usually controlled by a capacitor and resistor) and a flip-flop or similar. This circuit is about as simple as you can get, and is controlled by the charging and discharging of the capacitor. Though a 555 IC is easier to use and is dirt cheap.