CTCSS, it is common practice to turn off the CTCSS encode while the two-tone sequence is sent. This means system users with CTCSS decoders do not have to listen to the paging tones. Quik-Call I Quik-Call I, also known as 2+2, is a selective calling method originally used in one-way paging receivers. The Quik-Call name is a trademark of Motorola. It sends a pair of tones followed by 50 to 1,000 milliseconds of silence and then a second pair of tones. Decoders look for a valid first tone pair followed by a valid second tone pair within a defined length of time, (a time window). For example, a decoder detecting a valid first tone pair might allow up to 2 seconds for a valid second tone pair to be decoded. If no valid second tone is decoded within 2 seconds, the decoder resets and waits for another valid first tone pair. The system is less susceptible to falsing because it employs pairs of tone decoders that must detect valid tone pairs simultaneously. Quik-Call I is most famous for use in the fire service. The 1970s television show, Emergency!, depicted its use for base station ringdowns in the Los Angeles County Fire Department. In some systems, mobile radios had decoder options built into them. In Motorola mobile equipment, the decoders were housed in a box that bolted onto the radio control head. In the 1960s, it was also used to actuate tube-type receivers used to call out volunteer firefighters or to trigger sirens used to call out volunteers. Radios with Quik-Call I decoders may monitor all system traffic or remain muted until called, depending on the system design. When the radio receives the correct tone pairs in the proper sequence, it may momentarily buzz or sound a Sonalert. An indicator light may turn on and remain latched on. In most systems, the radio's receive audio would latch on if normally muted. In the Emergency! television show, the decoder turned on the lighting, activated the overhead loudspeakers, activated the horn/klaxon, and probably turned off cooking appliances. MDC-600 and MDC-1200 MDC, also known as MDC-1200 and MDC-600, is a low-speed Motorola data system using audio frequency shift keying, (AFSK). MDC-600 uses a 600 baud data rate. MDC-1200 uses a 1,200 baud data rate. Systems employ either one of the two baud rates. Mark and space tones are 1,200 Hz and 1,800 Hz. The