How I can make alarm on off?
The code you show will toggle the SPKR pin at a 1 Hz rate.  If you have an ordinary speaker attached, you will hear it click twice a second, but it won't generate an audible tone.

To generate a tone, use tone(pin, frequency) calls, or tone(pin, frequency, duration) calls.

For example:

void loop() {
   tone(SPKR, 400, 500); // 400 Hz tone for half second
   delay(500);           // no tone for half second
}


Note, ordinary speakers are low-impedance devices, eg 4 Ω, 8 Ω, etc.  You can use an audio transformer for impedance matching – this helps produce an adequate output volume – but lacking that, should put a resistor (eg 220 Ω) in series with the speaker to avoid over-current conditions.  AVR pins can deliver 25 mA without too much stress, and typically are rated at an absolute max of 40 mA.