It's been noted that the new matrix rules, in particularly the rules on detecting and locating silent running icons, make it dangerous/foolish to use matrix enabled gear on a run in any kind of a secure facility. I've been thinking about it, and I suspect it's not as dangerous as people suspect.
1) Decker-Spiders defending a site are likely to remain inside the site's host system, defending it's devices and firewalls, at least until an alarm is raised. This takes them "off" the local grid space, so they actually won't see icons moving around their building unless they have a reason to leave the host and go look for them. They instead see icons moving in the host, which is not the same. They might notice a hidden icon (like a Hacker) has appeared in their host, but they can't make check for hidden icons in physical space without exiting the host system. Additionally, many Spiders are actually not physically present at the build they protect, as their job can be done from anywhere via the matrix. This means if they happen to jack out they may not even be within 100 miles of the site, let alone within 100 meters of the Runners.
For building security, tracking wireless devices in the building would largely be handled through Radio Signal Scanners.
What this means: Unless you set off an alarm, or unlucky enough to arrive during a coordinated bug-sweep, no one is probably actively looking for hidden icons in the building. Your primary concern would therefore need to be the security systems: The Signal Scanners.
2) Radio Signal Scanners and Bug Detectors have a range of 20 meters, and are limited to only a single activity: Spotting Icons. Any matrix enabled device within 20 meters of an active radio signal scanner is subject to being spotted by it. If it's running in public mode, it's spotted easily, but if it's in silent mode, then the sensor operator gets to make an Electronics warfare + Logic [Sensor Rating] check. If the device has it's wireless on, it's rating can replace the Electronic Warefare portion of the roll.
It's unclear if a signal scanner can be left operating on it's own, but in theory it should be possible for a set of signal scanners slaved to a building host to operate continuously and most autonomously using their own rating instead of the electronic warfare of the spider, but probably getting the spider's logic. The sensors would be set to trigger an alarm, or at least an alert, to the Spider if they spot icons of particular types: Such as weapons or B&E gear. Remember: Standard matrix rules state that a device's icon reports what it is, more or less. It's unlikely that a building's spider wants an alert every time a janitor moves a bin full of Diet-Double-Choco-Tarts packages (each with an RFID tag) past a sensor at night, nor does he want an endless supply of alerts during the day as employees, each a bundle of matrix active devices and RFID tags, move around the building.
What this means: Signal Scanners can not be used to determine if there are un-spotted hidden icons in a building. Nor are they able to make Matrix Perception checks to investigate spotted icons, like verifying the icon is valid.
3) Spotting a Hidden Device Icon is an opposed roll which is defended with Your Logic or it Device Rating + Sleaze. Most devices/icons won't have a Sleaze rating, but the roll is still a defensive roll, so Full Matrix Defense applies. Runners of any stripe that knows they are passing within 20m of a Signal Scanner can use the Full Matrix Defense Action to add their Willpower to the defensive roll, which for some runners may make a world of difference. If you have all your devices slaved to a Commlink or Cyberdeck being owned/operated by someone with a good Willpower it may easily make up for the lack of Sleaze, or greatly enhance the existing Sleaze.
What This Means: Even without a sleaze rating, it possible to conceal an icon from a basic radio signal scanner. If the team has all their gear slaved to the Decker's Cyberdeck and backup commlinks (because cyberdecks have low device ratings and therefore can take many slaved devices) and he's using Full Matrix Defense, it should be difficult for a radio signal scanner to pick up any of their gear without dedicated actions by a Spider... which is unlikely as long as you don't trip any other alarms.
4) The Wrapper Cyberprogram can conceal an icon as something else, and can easily be run from a cheap Rigger Control Console. You could make your Chameleon Suit and Maglock Sequencer look like Choco-Tart wrappers: which are unlikely to trigger an alert if they are spotted by a Radio Signal Scanner. Net cost: $1650 ("Scatch Built Junk" RCC has a single program slot, + $250 for a single cyberprogram), every Hacker and probably infiltration expert should have one.
What This Means: Being spotted doesn't automatically ruin a run if you are concealing the icon as something else because the Radio Signal Scanner can't investigate, it only spots.
4) Radio Signal Scanners are just a security device on the site Host system. In much the same way you wouldn't walk in front of a security camera without the Hacker first looping it's feed, the team shouldn't wander around a complex with wireless devices before the decker has disabled or edited the alert setting for the radio signal scanners in the building. In most cases, I imagine the decker is gaining access to the building Host through a direct-connect hack, either on an accessible device in/on the building, or by getting a hold of a device slaved to the host that is more mobile (such as a smartgun brought home by the a security guard, against policy of course.) Once inside the host, the signal scanners are just as easy to hack as the security cameras.