Want to get a 9 volt transformer to use instead of 9 volt battery

I have these motion-detector-sprinklers to keep deer from my garden. There are 3 of them. The brand is called Scarecrow. Each of them has a 9 volt battery. I would like to be able to turn them off during the day, since the neighbors complain that they get soaked when they approach them. I thought I should get a transformer, a 9 volt transformer, that runs off of a 110 volt AC input, and run wires from the transformer to the 3 Scarecrows. Do I have to be careful what transformer I use? Can I get only one transformer or do I need 2? And is there any other issues (resistance, current) I need to think about?
Chuck

Do I have to be careful what transformer I use?

Be careful of the old style wall warts that use a transformer, diode bridge and filter caps. The output voltage that is specified on the case is often at full load. The problem is that the voltage can be significantly higher at lesser loads. So a 9V wall wart of 1 Amp can be 12 -14 (or more) at no or small load. Better are the switching power supplies. Their output is more stable over a range of output currents.

Current must be low or they can't operate off 9V batteries (I assume you mean those small blocks). A single 0.5-1A wall wart will do just fine.

Wiring: get properly insulated wires that are not too thin especially if the distance is large (talking about a large garden, deer and three sprinklers I guess you'll easily be dealing with 100 meters or more of wire). The kind you use for light is fine, 2x0.5 mm2 will be more than enough. This wire has very low resistance, but the thick core also makes sure it doesn't break easily. Use an outdoor version if you want to dig it under.

The "secret" is, search for a DC power supply. (Transformers are AC.)

[u]Here are some from Jameco[/u].

You probably don't have to worry about the current (or power) rating, since 9V batteries don't put-out much current. A "regulated" power supply will hold the voltage constant (as long as you don't exceed it's current rating).

You probably will need to cut-off the connector and maybe add some [u]battery connectors[/u], and it would be helpful if you have a multimeter to check the polarity.