I want to replance a standard wall switch (2 wires: white & black) with a PIR Occupancy Sensor switch

SOURCE: Trying to replace Intermatic with Utilitech inwall

The wires on your new switch are intended for black = power .. white = neutral . and red = lights .. with two black wires on the old switch I am assuming that there is a bundle of white wires in that wall box, the white timer needs to join that bundle ... then you need to determine which black wire is the power from the electrical panel ( voltage tester) and connect to the black timer wire .. the red timer wire connects to the other black wire in the wall..

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SOURCE: I bought a Utilitech 7 day digital in wall timer,

HI .. if the switch has only a black and white wire attached, and there are no other wires in the wall box, then you cannot use this timer switch. You need to return it and get a timer that does not use a neutral connection. The wires you have are a switch leg from the light and there is a white wire but it is not a neutral.
If there are other wires in that wall box , tell me and we can chat more about how to remedy this .

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SOURCE: Utilitech Wall Timer #0192773 does not switch

Old timer: Intermatic EJ500 & ST01C timers have a battery. Battery operates the clock motor. Red wire is for 3-way circuit [a hallway with 2 switches is a 3-way circuit].

Utilitec timer, clock runs on 120Volt circuit instead of battery. So clock has to have power.

How to connect wires:
Black timer wire connects to hot wire from breaker box.
Red (or blue) timer wire goes to landscape lights.
White timer wire connects to white neutral wire [or if no neutral is available, connect to bare ground wire].
Green timer wire goes to bare ground wire.

How to find black hot wire and white neutral wire inside box: Disconnect and separate wires so you can test. Use ordinary tester. Power is on. There is only 1 black hot wire inside each electrical box. Test each black wire to bare ground until tester light comes on > that identifies the black hot wire. Next, test black hot wire to white wires until tester light comes on > that is the neutral wire. Exception: This test does not necessarily work with 3-way switches since they reverse each time switch is thrown.

SOURCE: GE digital timer. Instructions say to: 1)

Find the Hot wire:
Your switch has 2 wires. One of these wires is Hot, and one goes to load. Disconnect wires from switch. Turn on power. Do not stand on wet surface. Test each wire to bare copper wire. When tester lights up, that is Hot wire. The other wire goes to load.

Connect wires:
Hot wire goes to Black timer wire
Wire to load goes to Red timer wire
White wire connects to white wires that are twisted together
Bare copper wire connects to Green wire from timer

How to connect white wire to white wires that are twisted together.
a) Strip white timer wire so you have 1-1/2 " of bare wire. Stranded wire will wrap around other wires easily.
b) Remove wire nut. DO NOT UNTWIST wires.
c) Hold all whites together so bare copper lines up. Wrap stranded copper around the twisted wire.
d) Replace wire nut, or use larger wire nut. Twist real tight. Do not use tape. You can solder the connection.
e) When done, pull on white time wire to make sure it is held tight. Push whites back into box.

SOURCE: I have a ge digital

I have test-wired your timer, and many other timers.
Your white and red together are causing the clicking.

Hot from breaker connects to timer-black.
Wire going Load (lights) connects to timer-red
Timer-white wire connects to Neutral inside box.
In your case, you don't have the neutral so connect the timer-white to bare ground wire.

add a comment if you need more help.